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.

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

Common Software Problems

Excel can have problems dealing with add-ons. Visit 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:


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, which talks about this.


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’ : Missing Reference Errors

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.

1,829 thoughts on “Help”

  1. Hi,

    I had set-up a LP for 3D bin packing.
    The default optimization algorithm provides a sub-optimal solution.
    While Satalia is working fine.

    Any thoughts on what could be possibly causing this.
    Scale of problem is

    1. It could be tolerances for CBC? Try setting the integer tolerance to be 0%. Hope this helps; please let us know. Andrew

  2. Dear Team Open Solver,

    Hello my name is Gilang. I try to solve Travelling Salesman Probelm using Open solver. Because I’m new user of this program, could you give me some guideline to solve Travelling Salesman Problem to minimize cost?.
    Thank you.



  3. Hi for Argentina,
    Your Solver helped me a lot with my hospital schedule project.
    The lineal way works well but I’d like to solve it in a non-linear way for better performance.
    I’m using a Mac,
    I downloaded everything well as described but when I try to solve it in any non-lineal way, a message pops up saying :
    “Error 94: Utilisation prohibited of Null

    Solver: Bonmin

    CBC v2.9.4 (64-bit) at “/Library/OpenSolver/Solvers/osx/cbc”

    No Gurobi installation was detected. The following file was not found: “/usr/local/bin/gurobi_cl”

    Bonmin v1.8.4 (64-bit) at “/Library/OpenSolver/Solvers/osx/bonmin”

    Couenne v0.5.6 (64-bit) at “/Library/OpenSolver/Solvers/osx/couenne”

    NOMAD v3.7.1 (64-bit) using OpenSolverNomad v1.3.1 at “/Library/OpenSolver/Solvers/osx/OpenSolverNomad”

    Seems like OpenSolver cannot find the file required.
    Any advice to give me? I’d really like to solve it in a non-lineal way.
    By the way, thank you so much for “OpenSolver”. I’m an Industrial Engineering Student and I just had a conference about that hospital schedule I solved in a lineal way. I took permission to spread your information for about 100 engineering students.

    1. You have a formula in your spreadsheet that we cannot understand. Please try simplifying it. Andrew

  4. I built a linear scheduling program (similar to the nurse rostering problem) that works great with the COIN-OR CBC engine except for one problem: for continuity, employees need to be scheduled for as many consecutive shifts as possible (up to a limit of 4 consecutive shifts). Any suggestions for how to incorporate this preference for consecutive shifts would be appreciated, perhaps using a non-linear solver engine? Here is a link to the sheet I’m working with:
    Thank you!!

    1. I run a research programme in nurse rostering using optimisation. We use a technique called column generation to capture complex preferences of the type you are describing. It is harder to do this using standard integer programming. One approach is to blend a set-covering model with a network flow model (which I have done before), but again, these are technically hard models. If you need consulting expertise, I can point you at our local modelling guru. Cheers, Andrew

  5. How do i perform sensitivity analysis for the the integer programming, after using COIN or CBC (liner solver), it just gives decimal result and stops with error that Sensitivity cant be performed due to integer constraint.

    1. You can’t sorry. Sensitivity analysis is very different with integer variables. Andrew

  6. Is it not possible to disable the window:
    “Opensolver could not find an optimal solution, and reported:
    No Feasible integer solution

    The solution generated has been loaded into the spreadsheet”

    How can I work around this window to avoid it poppin up. the disableevents and disablealerts do not work!

    1. You should be able to disable this. Please check the VBA code. If you cannot disable this then that’s something we need to fix. Thanks, Andrew

  7. Hello,

    I am using the OpenSolver add-on in Google Sheets. I used to get functionality, messages, errors, etc. but now it just goes “grey” and is frozen and unresponsive. I have removed the add-on and added it back and still no change. I am not sure what has happened.

    1. Not sure why that is. Perhaps you could try this in a different browser? And with a different Google logon? Sorry we cannot be more helpful. Andrew

      1. Andrew,

        Thanks for getting back to me.

        I think the issue stemmed from importing an Excel Workbook into Sheets (so I didn’t have to re-do) the calculations and formatting. I started fresh and saw no issues.


  8. Greetings Open Solver team!
    I received the following error message:
    Error -2147220504: NEOS was unable to solve the model because there was an error while running AMPL. Please let us know and send us a copy of your spreadsheet so that we can try to fix this error.

    I have sent a copy of the spreadsheet and would appreciate any thoughts you might have. Thanks!

  9. Hello,

    I have been trying to put in decision variables from multiple sheets but it keeps giving me an error message saying that I should follow excel’s internal character limit. I have tried to shorten the names of each sheet but to no avail. Is there any way I can use decision variable tables from multiple sheets?


  10. Any thoughts on why the (or any version for that matter) is being flagged by our corporate security platform as containing a trojan?

    1. The anti virus packages get this wrong every now and again. We have on occasion made somewhat random code changes that have removed these warnings, but don’t do thks anymore. You can use to check any file using a wide range of virus tools; this will show that our files are clean and that some tools are too zealous and give false reports. Andrew

  11. Hi,
    I have a LP problem with ~2400 variables & ~500 constraints. Would opensolver be able to handle this ? I am not able to find anywhere the capabilities of open solver on this page.

    Regards, Shantanu

    1. That is probably not a difficult L.P. to solve. If it is an I.P. it may be harder. It all depends on your particular problem. OpenSolver has no imposed size limits and so you should try it out on your problem. Andrew

  12. Hello

    I have been using Open solver for many weks , regularly and today it suddenly broke down and does not work an more

    So I tried various chnges , but do ot recover working

    Nothing happens any more when I click solve model
    I heve been trying all kinds of solver in the dropdown list

    Please can you help me because i do rel on it know

    Thanks in advance

    1. Most odd. Please download OpenSolver again to get a new clean copy. If that doesn’t work try repairing your Excel installation. Hope this helps. Andrew

    2. Something like this is happening to me too. It was working well for a week and I was stepping up to larger and larger linear programs. Now I click ‘Solve Model’ and it goes gray and has the spinning bar, but doesn’t give updates on progress so I can’t tell if it’s working. I tried various things such as re-creating my program on a new sheet but it comes out the same.

      Before this, there were several instances where it was interrupted from internet disconnecting or maybe my computer going into hibernation. When I re-opened, it gave a message asking if I want to resume progress or start over. I think I tried both options at some point. After the 2nd or 3rd time being interrupted it stopped giving the message so I wonder if that is related.

      I will try starting over with a clean copy of OpenSolver.

    3. After it got bogged down I tried to remove and re-add Open Solver but it kept doing the spinning without progress. I tried re-creating my program under a new Google sheets and now it seems to be working like normal again.

  13. Hi Team,
    We have set up an optimization model using OpenSolver for maximizing the revenue. The model is dependent on some options selected by the user and this varies the number of rows of data under consideration for the constraints as well as the decision variable. Currently, we have set it up with additional buffer rows and this slows down the optimization process and puts us at a risk when the buffer falls short. Is there a method to set the range of the constraints and the decision variable as dynamic for both sides of the equation?

    Best Regards,

  14. Hello,

    Is it possible to write a macro to execute the solver on models across multiple worksheets in one Excel file?

    I have the same model on a large number of tabs and would love to click a Macro button to run them all in succession.

    Thank you,

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