Help

Welcome to the OpenSolver on-line help.

We hope that most of your questions will be answered on the Using OpenSolver page. However, if you still have a question, please post it below.

As of July 2025, there are two known issues caused by Microsoft code changes. These are a RefEdit issue that breaks the Model dialog (see #6 below; a user can easily fix this) and a DLL access change that impacts NOMAD (see #10 below; fixing this requires editting VBA code).

Building  Linear Programming models

Writing optimisation models that only use linear mathematical equations and inequalities is not easy. However, most of the time you want to build these “linear programming” models (and avoid non-linear models) because these are easier and more reliable to solve using packages such as OpenSolver. (OpenSolver uses CBC by default to solve these linear programmes.) Check out this Wiki page on linear programming.

The AIMMS folks have a great online chapter describing how to take non-linear requirements (local copy of pdf) and model them using linear programming. (Thanks to Stu Mitchell of PuLP fame for pointing out this resource.) The NEOS guide is also a great resource. If you still have a modelling question (e.g., how do I express this requirement using the rules for a linear program), please ask it on https://www.or-exchange.org/.

Common Software Problems

Excel can have problems dealing with add-ons. Visit http://www.add-ins.com/how_to_repair_office.htm for a guide on fixing these.

1. OpenSolver not loading – July 2016 Office update (no error message)

In July 2016, MicroSoft released an update to Office 365 which prevents OpenSolver from loading unless the .zip file is “unblocked” before the files are extracted. (We expect this change to appear in other versions of Excel.) The symptoms are simply that OpenSolver does not appear in the Data tab; there is no error message shown. To fix this, delete your old OpenSolver files (but not the downloaded .zip file), right click the downloaded OpenSolver .zip file, choose Properties, and click the Unblock button which will show if the file is blocked. Once the file is unblock, close the properties dialog, and then un-zip the files and open up OpenSolver.xlam as usual.

2. Unable to find the external solver …

If OpenSolver reports this problem, then it could not find a solver file that comes with OpenSolver. Please check that you have extracted (i.e. un-zipped or uncompressed) all the files from the OpenSolver download.

3. The solver did not create a solution file.

If this error is reported, then it is likely that OpenSolver was unable to run the solver executable. This may happen if the OpenSolver files  are in an ‘untrusted’ location, and so Windows will not let them be run. First check whether the solver is shown as found in the “About OpenSolver” form. If not, go to the folder identified in the “About OpenSolver” form and double click on this solver file. You should then see a command window open that gives the solver name and version information etc. If you don’t see this, then Windows should give you an error message to help you diagnose the problem. It may help to move the OpenSolver folder (and all the files it contains) into a location such as your Documents, or even into Program Files, and try again.

4. Solver crashes; OpenSolver reports no solution file

The files in the “Solver” folder provided with OpenSolver contain the actual solver code. These solvers are being continually upgraded as bugs are reported and fixed. If OpenSolver reports that no solution file was generated, then the solver may have crashed. This can happen on big problems when the solver runs out of memory, but also on smaller problems that happen to hit a solver bug. In such cases, you should check if a newer version of OpenSolver is available since we regularly update the solvers included with OpenSolver as they are released.

With CBC, a typical OpenSolver error for thois problem message might be: ‘The CBC solver did not complete, but aborted with the error code -1073741510’

If needed, you can download the latest version of CBC, Bonmin or Couenne from AMPL. Download the either the Windows or Mac version as appropriate. For Windows, get the 32-bit version if you have 32-bit Windows, or the 64-bit version otherwise. (The 64 bit version will solve much larger problems than the standard 32 bit version included in OpenSolver, so always choose this if possible. Right-clicking on Computer, and choosing Properties, will tell you if have a 32 or 64 bit system type.) Right click on the downloaded .zip file, choose Properties, and click the Unblock button if there is one. Then, open the .zip file, and drag the files into the right location in your OpenSolver Solvers folder (the win32, win64 or osx folder as appropriate), replacing the existing files. This may fix your problem.

Report a CBC bug

If after installing the latest version of CBC, CBC still crashes on you, then you may wish to report a bug. Please be sure to include the .lp file produced by OpenSolver; you can open this file using “View Last Model .lp File”. CBC bugs can be reported by either:

  1. The online CBC TRAC bug reporting system (which you will have to register for), or
  2. The CBC mail list

Switch from CBC to Gurobi
Since August 2014, OpenSolver has also supported solving models using the Gurobi solver. You can obtain a copy of this solver at no charge if you are at a university. Gurobi is faster and more stable than CBC, and comes highly recommended.

5. Repairing Excel

Sometimes it is useful (if all else fails) to repair your Office installation:

Windows

See these Microsoft Office 2010 and later instructions (or in Excel 2007, use Excel’s application menu, then Excel Options, then Resources, then “run Microsoft Office Diagnostics”). You might also want to look at http://support.microsoft.com/kb/166273, which talks about this.

Mac

Unfortunately there is no easy way to repair the Office 2011 installation. The best option is to follow these instructions to completely uninstall Office. You can then install Office again from scratch to get a clean version installed.

6. ‘Can’t find project or library’ and ‘Compile error: variable not defined’: Missing Reference & Blocked ActiveX RefEdit Errors (updated July 2025)

July 2026 update: OpenSolver uses the ActiveX “RefEdit” control.  If this is not accessible, then you may get a “compile error: variable not defined” error (at a line containing “refObj”) when you open the Model dialog. I have also had a “Run-time  error -2147352573 (800200003)  Could not find the specified object” occur when clicking the “Model” button.

According to StackOverflow, the default setting in Excel has recently changed to a stricter level and this disables controls from external libraries like RefEdit. So, in recent Excel versions, permission to use ActiveX controls must be turned on in the Excel Trust center. To do this, use File…. Options… Trust Center… Trust Center Settings to select “Prompt me before enabling all controls with minimal restrictions” (with “Safe mode” turned on); see this screenshot. (Thanks to jkpieterse for replying on StackOverflow with this information, and for Ziad for sharing the settings that worked for them.)  It also works for me selecting the slightly safer “Prompt me before enabling Unsafe for Initialization (UFI) controsl ith additional restritions and Safe for Initialzatrion (SFI) controls with minimal restrictions”. Note that this change also causes Frontline’s Solver to crash with the error “Solver: An unexpected internal error occurred or available memory was exhausted.”

OpenSolver uses the “RefEdit” control, which we need but which can cause problems because of missing references caused by version changes. To check for missing references, using the VBA editor (which you access using Alt-F11), select OpenSolver (openSolver.xlam) in the Project window, choose Tools… References, and look for a “Missing:” line. If you see this, un-check that line, close the dialog, and choose File … Save OpenSolver.xlam to update the file. If this doesn’t help, try the above steps for repairing Excel.

7. Error 70: Unable to delete the file: C:\Users\XXXXXX\AppData\Local\Temp\log1.tmp

This errors happens if Excel crashes while OpenSolver is running, leaving log1.tmp open. Please restart your computer, which will close this file, and try again.

8. OpenSolver was working on my Mac. Then I updated to Excel 16.16.7 (released late 2018) and OpenSolver stopped working. What do I do?

We have had numerous users report this issue. We are looking for a Mac user with VBA experience to help us diagnose this problem. Please contact us at email hidden; JavaScript is required if you can help.

9. OpenSolver does not work in Excel installed from the Windows Store

Windows Store versions of Office applications do not support Add-ins such as OpenSolver; see this link, or this support page for another add-in, or this technical article from Add-in Express. This Dell article explains a little more. If you have a Windows Store version, it will display this in the Excel Version information, such as in the following example:

Version 1807 (Build 10325.20082 Microsoft Store)

The solution is to un-install Excel, and install the click-to-run versions, in which case the Excel version will change from ‘Microsoft Store’ to ‘Click-to-Run’. Standard installs (meaning not Office 365) don’t have this issue.

10. “About OpenSolver” menu crashes; NOMAD crashes (updated July 2025)

July 2025: A recent update to Excel has blocked access to the “OpenSolverNomad.dll” file that we use to execute the NOMAD solver. Symptoms of this include the “About OpenSolver” window crashing with an error: Run-time error: ’53’: File not found: OpenSolverNomad.dll
(This error occurs even though OpenSolverNomad.dll is located in the Opensolver folder under Solvers/win32 and Solvers/win64.) OpenSolver Errors also occur when trying to use the NOMAD solver.

These errors occur because Microsoft have restricted Excel’s access to DLL’s (which is what we use for Nomad). To fix this in OpenSolver you need to edit the code. (We will release a fix at some stage.) For more information, see this Microsoft Community post (also available locally). One of our users, Ed, says “I can confirm that adding the full path in the [NOMAD DLL] declare statement works”. See also this StackOverflow post.

Note: This has been confirmed for “Microsoft® Excel® for Microsoft 365 MSO (Version 2507 Build 16.0.19029.20136) 64-bit” installed as part of “Microsoft 365 Apps for Enterprise” on 12 Aug 2025.

2,231 thoughts on “Help”

  1. In the last 24 hours, OpenSolver add-on in Google Sheets is opening but showing up blank. Anyone else running into this issue?

    Reply

  2. Is there currently a problem with Open Solver add-in for google sheets? when i open the side window nothing comes up. i have tried from different machines, with no luck.

    Reply

  3. Hi
    I’m attempting a non-linear solution using the 2 options in the install ie Neosbon and Neoscou for a rather complex problem but each time I run it (either engine) I get the same error:
    Type mismatch (at line 5404)(at line(5138)(at line 4840)(at line 7144)(at line 2186)
    Source=OpenSolver, ErrNumber=13
    It takes a long time to get here (1+ hours) with the spreadsheet contents not displayed after about 2 mins (ie like there is no open workbook) and a status line something like:
    OpenSolver: Constraint progress: 0/8. Processing formula 2/2. Current formula progress:800+/1687.
    Any ideas or is it just too complex?

    Reply

    1. Sorry it is not working. Please send your sheet to email hidden; JavaScript is required so we can diagnose this. Thanks. Andrew

      Reply

    2. James, did you have any luck with this? I also am getting the same error. With Alldif not being an option, I tried to create If,0,1 across multiple cells then constrained those to 0 as a workaround but it did not work. Anyone I can email my model to to take a look? Using the Mac version

      Reply

  4. Hi… i have a problem with run opensolver on win 8.1 64 bits excell 2010. the message

    —————————————————————
    Opensolver 2.6.1. encountred an error:
    Unable to run the external program:
    C:\Users\RODRIGO1\AppData\Local\Temp\cdc.bat

    Error 5: Acceso denegado. (At Line 1448) (At Line 2810)

    Source = OpenSolver , Err,Number= 2147220500
    —————————————————————

    PLEASE HELP!!!!!!!!!!!

    Reply

    2. Please confirm it is cbc, not cdc, in the error message. Assuming it is, please try running this model again (which will give the error message again), and then open the folder “C:\Users\RODRIGO1\AppData\Local\Temp” and check that the file “cbc.bat” does exist. Then try double clicking it, and seeing if it runs. (You should get new output files written in the same directory if it works; and sort by date and then press F5 to see these.) If it does not run, then your PC is configured not to run .bat files out of temp folders. In this case, please try an old version of OpenSolver (2013 or earlier should be safe). Sorry this is not working as smoothly as we’d like. I look forward to hearing how you get on so we can improve this in the next release. Andrew

      Reply

  5. Hi,

    This could be a question with a blindingly obvious answer (and I hope it is) but how do you generate an answer report? I can find the sensitivity report without a problem but I can’t work out how to generate one. Can anyone help?

    Thanks!

    Belinda

    Reply

  6. Am going up the learning curve with open solver.

    I am not able to add more than 25 variable cells, even holding down Ctrl — what am I doing wrong?

    Regards

    Reply

  7. I have been using this amazing program since January of this year and it has been working great… until last night. Late in the evening, during the normal running of my project, I suddenly received the following message: “OpenSolver2.6 encountered an error: Permission denied (at line 2810) Source= OpenSolver, ErrNumber=70”. Subsequent attempts at re-opening and rerunning the project yields the same error. Again this morning, the same error is appearing each time I attempt to run my project.

    Nothing has changed within my project as I have been running this exact model since 05 February, 2015. Prior to last evening, I always received a solution when running my project. It ran perfectly fine earlier in the day??? Are there any ideas as to what has caused this problem given the error data provided?
    Sincerely,
    Daryl G

    Reply

    1. You are our second report of this problem. Do you mind seeing if it works again of you 1) restart excel or 2) restart your PC. Sorry about this… we maybe leaving a file open in some circumstances… your help to find this would be great. Andrew

      Reply

      1. Andrew,
        A complete system restart was required – closing and restarting EXCEL only was unsuccessful. Now, everything works just as it previously did. I have to say that I am greatly appreciative of this software! It is AMAZING!!!
        Daryl G

        Reply

        1. Thanks for the feedback. It certainly sounds like a file being left opened; we have made changes to track this better and will include these in the next release. Andrew

          Reply

  8. I am using opensolver to Optimize the scheduling problem for a 24/7 call center. There are around 5000 variables and 2500 constraints… Everytime when I run the model, it was stuck at “writing model to disk” and stopped there. Is there any way to improve this?

    I have not been able to get this scheduling model resolved, however, other smaller models work for me. Any suggestions would be appreciated.

    Reply

    1. Sorry to hear of your problems. That’s an unusual bug; haven’t had that complaint before. Please confirm you are using the CBC solver (i.e. the standard download, not the experimental advanced one). Please check you have the latest version (2.6.1), and then try running with the “show optimisation progress while solving” turned on to see if CBC is taking a long time. (If it is, then we need to improve our status reporting). Andrew

      Reply

      1. I am trying to get a solution for a daily assignment problem where I want to fairly allocate better/worse working positions to my employees and I am also experiencing the same issue but with OpenSolver 2.8.5 Advanced. It seems to happen if I use either bonmin or couenne. The option “show optimisation progress while solving” is on. At the end of the job it hangs Excel at “writing model to disk… 381 vars, 131 rows.” and the only possibility is to force close Excel.

        Any ideas?

        Thank you.

        Reply

        1. Sorry it is not working. Do you mind sending the spreadsheet to email hidden; JavaScript is required? Please include a copy/paste copy of the text of teh ABout OpenSolver dialog. Or, if you know VBA, you can step through the code to see where it is getting stuck… Andrew

          Reply

  9. Sorry – basic installation proble. managed it successfully on home pc (Office 2013 and Win 7) but failing at work (office 2010 and Win XP)

    It is the old “cannot find cbc error”.
    Have followed the advice given on this page and copied the ZIP to a folder and double-clicked on the add-in.

    “About OpenSolver” output is as below and the cbc.exe is in win32 and can be run to give a cmd window:

    Unable to find CBC (‘cbc.exe’) in the Solvers folder.

    No Gurobi installation was detected.

    Unable to find NOMAD (OpenSolverNomad.dll) in the `Solvers` folder (\\customer\userdat$\newington\Croom3M\OpenSolver2\Solvers\win32)

    Unable to find Bonmin (‘bonmin.exe’) in the Solvers folder.

    Unable to find Couenne (‘couenne.exe’) in the Solvers folder.

    OpenSolverFile: \\customer\userdat$\newington\Croom3M\OpenSolver2\OpenSolver.xlam

    Reply

    1. Sorry to hear it is not working. We have never tried installing via a network share (i.e. a “\\…” path). Please try installing on your own hard disk, and let us know if this works. Thanks, Andrew

      Reply

  10. Hi, I am trying to build a flexible model with a “standard” of 10k binary variables and about 12k constraints, which all needs to be run through VBA modules, but I’m having difficulties with assigning variables and constraints to the model from VBA. My attempts so far have been to use the commands for the Solver (i.e. SolverAdd), but I can’t make it work (which I assume to be due to the limit on the standard Solver). I’ve been poking around in the OpenSolver code without being able to find a solution. Is there no way to load variables and constraints directly into the OpenSolver? Any help will be most appreciated!

    Reply

    1. We don’t have any nice API for building a model (and instead recommend you build it on the sheet yourself if possible). However, based on feedback from others, the Solver VBA methods should work (but note I have not tested this). Alternatively, you can create the Excel names yourself that store a model – installing Name Manager will show you these. Sorry we cannot be of more help. Andrew

      Reply

  11. Hi all,

    I’m getting the error:


    You have the 'ignore integer constraints' option turned on. Please turn this off
    and start OpenSolver again or choose OpenSolver's solve relaxed model option (at
    line 1045) (at line 2806)

    Source=OpenSolver Model Build, ErrNumber=-2147220504

    Actually, I don’t know how to turn this off. Moreover, even if I run the relaxation, I keep getting this error.

    Thanks in advance.
    Toby

    Reply

    1. Thanks… we need to report this more clearly. Please turn off the solve relaxation option in the Solver options dialog (i.e. Solver’s options dialog, not OpenSolver’s) and try again. Andrew

      Reply

      1. Thank you Andrew. Now it works flawlessly. Your AddIn is great. Now I can solve most problems with Excel.

        Keep up the great work
        Toby

        Reply

  12. Hello all,

    First of all, congratulations on a job well done coming up with such a great application. It is nice to see that there are still people out there who help out others altruistically …

    Anyway …

    I am trying to find optimial solutions to a model in Excel, which is almost entirely based on discontinuous and non-smooth functions. Regrettably, I am unable (or incapable) of simplyfing it to a linear model. I have tested the model in the limited Excel Solver and I managed to get out some decent results with the GRG Non-Linear and the Evolutionary Engine.

    I tried to do the same with the Bonmin and Couenne Engines on OpenSolver, but I consistenly get the error “unknown associativity=neg”. Is this error caused by a specific formula or something in my setup? I also tried the NOMAD engine, but I get the following error:

    OpenSolver2.6.1 encountered an error:
    There was an error while Nomad was solving. No solution has been loaded into the sheet. (at line 7040)(at line 2810)
    Source =OpenSolver Nomad Model Solving, ErrNumber = -2147220492

    I was also wondering if there are plans to implement GRG or Evolutionary Engine in Open Solver.

    Thank you very much for your time. I hope my question can help others.

    Regards,

    Vasil

    Reply

    1. Vasil: Thanks for this error report. To help us fix this, can you please email us your s/sheet to a.mason at auckland.ac.nz. Thanks also for the positivbe fe3edback, and sorry about the problem you have uncovered.
      Andrew.
      PS: We are happy to connect to any solvers that are AMPL compatible. However, I don’t think there is such an Evolutionary Engine (or a Genetic Algorithm (GA)) that works with AMPL… perhaps we could look at adding a GA in the future, but it would b a bigger job.

      Reply

  13. Hi Andrew,

    I get an error when trying to solve a model using [NEOS using Couenne (Non-linear solver)]. The error message is as follows:

    OpenSolver2.6 encountered an error:
    No cells were found. (at line 4889) (at line 7144) (at line 2816)
    Source= Microsoft Excel, ErrNumber=5

    Could you please tell me what it means?

    Thanks in advance.
    Alex

    Reply

    1. Alex: Would you mind trying our latest 2.6.1 release? If the error still occurs, then please email us your spreadsheet to a.mason at auckland.ac.nz so we can diagnose the problem. Thanks for the bug report. Andrew

      Reply

  14. Hello,

    I am having issues with selecting disjointed ranges as the variable cells. I have tried separating the ranges with commas and semi-colons, but each time I select the second range, it deletes the original range I selected. Am I missing something obvious?

    Best,
    Matt

    Reply

  15. I have a problem with an allocation problem that i could solve with the excel’s original solver but opensolver doesn’t.
    can i send you the excel file to see if something wrong with the model?

    Reply

    1. Sorry to hear it is not working. What, exactly, is happening when you try to solve your problem? And can you solve it with the free Solver built into Excel?

      Reply

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