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.

Excel can have problems dealing with add-ons. Visit for a guide on fixing these.

Common Problems

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.

1,347 thoughts on “Help”

  1. Hello,
    I am struggling to access the nonlinear solvers provided within OpenSolver. Where do I download the bonmin.exe for the COIN-OR Bonmin Non-Linear solver to run it within excel? When I attempt to access the NEOS using Bonmin solver it states that it cannot connect to the NEOS server at this time. Do all of the non-linear solvers leverage a third party to find the solution? If so how efficient (time-wise) are they at returning solutions. I am looking to iterate through a loop solving multiple problems.

    Thank you so much for taking the time to answer my questions.

  2. Dear,

    Would it be possible to use OpenSolver in excel to solve a relatively large linear program.
    I want to solve an linear program with about 175 000 variables and 200 000 constraints. Would this be feasible with OpenSolver?

    Thank you,


    1. It would be very slow to get the model out of the spreadsheet; I’d use SolverStudio instead. Andrew

  3. Hello.

    I’m having problems in using OpenSolver in project I made. Everytime I get an error. Or “Invalid procedure call or argument”, or “One of the parameters supplied to NOMAD was invalid. This usually happens if the precision is too large. Try adjusting the values in the Solve Options dialog box.”.

    When I use the Engine NEOS using Bonmin, I get this error:
    “OpenSolver 2.8.5 encountered an error:
    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.

    An error log with more details has been saved, which you can see by clicking ‘More Details’. If you continue to have trouble, please use the ‘Report Issue’ button or visit the OpenSolver website for assistance”

    Maybe I’m doing something wrong. Can you help me?


    1. Sorry it is not working. Do you intend to be using a non-linear model? We recommend linear models if at all possible. Your spreadsheet will have formulae in it that OpenSolver’s solvers cannot understand. You cannot use any formulae such as vlookup etc. Please check the s/sheet carefully, and send us a list of the formulae you are using. The NOMAD issue is not so obvious to me; are you using the default parameters? If not, perhaps you could send us the sheet to email hidden; JavaScript is required. Good luck, and Merry Xmas. Andrew

  4. Hello,
    What engine I can use to find out minimum (maximum) value of a function f with linear constraints:
    f = x1 * x2
    where x1 – variable of type binary
    x2 – continuous variable

  5. I am rather hesitant about bothering you with my queries concerning Open Solver, considering my very low level of ability to use Excel.
    I am attempting a numerical solution of a problem dealing with the behaviour of voids in worked metal billets. I can reduce this to a system of nine non-linear equations, one of them a fourth order polynomial, one a non-linear function of circular trigonometric functions, the remainder second order poynomials. None is particularly complex mathematically. I have kept the analysis at a relatively elementary level and am trying to avoid elevating solution of the equations into a major phase of the investigation because it may be argued that the physical model I have adopted does not justify it. In turning to Excel, I am unclear what ad-on(s) to Excel (currenty Excel 2007, but to be raised to the 2016 version shortly, I believe) I would need for solution of these non-linear equations. I note concerning your comments on NOMAD that all the constraints are necessarily equality constraints (to satisfy the requirements of yield) and that good bounds to the geometrical variables are difficult to estimate. I cannot assign much significance to the numerical values I may obtain, although a good prediction of trends would be very valuable fundamentally and in industry.
    I would very much appreciate it if you were to suggest what you think one of your OpenSolvers may be suitable, and with what software.
    I would like to add that I was emboldened by the generous approach which you are so evidently taking in sharing your software.
    Best regards,
    Peter Thomson

    1. Peter. I would suggest you set up the problem to minimise the sum of squared errors between the left and right hand side of your equations, and then minimise this sum of squared errors using Solver, or OpenSolver with NOMAD (which may work), or BONMIN or COUENNE. Good luck; sounds like an interesting project. Andrew

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