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.

1,419 thoughts on “Help”

  1. I found what was slowing down model setup … the indirect function. I had named cells in one range (say with names x, y and z) containing model input data and had these names listed as text in a second range (say in cells c10=”x”, c11=”y’ and c12 = “z”) and was using indirect(c10), indirect(c11) and indirect(c12) in a third set of cells (say in cells z100, z101 and z102) to show the data in named cells into the third area. Yeah its kinda complex … but really slowed down model setup. When I deleted the indirect statements setup time was back to normal.

    1. Thanks for letting us know; this will be very helpful for other users trying to speed up their models. Keeping the formulae simple is always best if it is possible. This is because we evaluate the spreadsheet many times (once per decision cell) to set up the model. Cheers, Andrew

  2. I’m using OpenSolver for a binary scheduling model. If OpenSolver is unable to find a feasible solution given the input parameters and constraints, does it return the best alternative with constraints relaxed, or does it return whatever was the last set of conditions it was testing?

    1. It returns whatever the solver returns, which is rather random. It does not relax the constraints; this is something you would need to do by adding extra variables, one per constraint, and then penalising these in the objective function. Good luck, Andrew

  3. Hi, my problem is about “Unable to delete the file”

    The screen displayed “: C:\Users\刘兆邦\AppData\Local\Temp\”. And I do not have the log1.tmp.

    Opensolver had worked last week. But this week it is not working.

    Could someone help me to fix this?


    1. I suspect that VBA won’t like the non-English characters in that path. But that should have been true last week as well (unless you have changed the logon name?). If the file is open, then re-booting may allow OpenSolver to delete it. Please try re-booting first, and then loggin on with another user name; please let us know how you get on. Andrew

  4. Hi,
    I’m trying to optimise the choice of a PLC and it’s modules based on price. There are 3 types: one that doesn’t support additional modules, one that supports 2 and one that supports 8. I’m trying to add a variable that if “activated by user” B13 (1 or 0) that forces the optimisation to leave room for at least 1 more module.
    I’m getting this error:
    “…The model contains ‘AM14=1’ for which instance 1 does not depend on the decision variables and is not satisfied.
    Constraint specifies: LHS=AM14=1 = RSH=1=2…”
    I don’t get why at RSH is says 1=2.
    And i have configured this function AM14=IF(OR(AND(B13=1,AM10>AM52),B13=0),1,0) where B13 is my input, AM10 is max configurable modules and AM52 is currently configured modules (both are automatically calculated). The constraint is AM14=1.
    The constraint depends on the input since the curent number of modules configured depends on the variables. What am I doing wrong?

    1. This is not a linear model, sorry. Try Googling “MIP formulations”. Good luck, Andrew

    1. Yes free to use. It is under the GPL and so any changes to our VBA code need to be shared in source code form if you publish/sell the modified code. Andrew

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