I got this problem after adding a combobox with VBA-code in a particular sheet. Testing the code etc was no problem at all, until I opened the sheet again. Stackoverflow and Microsoft comes with many work arounds, but no real solution. I use excel 2010 (dutch version) with W10 (upgraded from W7). I think the problem is in Excel 2010. In my case, I got an error on the line to unprotect a sheet by VBA, in a module which wasn't changed for a long time.
Ok, this is how it is in my opinion: There was a security issue in FM20.DLL, for whic MS had an update in Q1 2015. This update installs a new FM20.DLL, however the language packages (FM20NLD.DLL and FM20ENU.DLL) were not updated. Possibly, if you don't use a language pack, you don't have this error. In my opinion, the language parts should have been updated as well (but there is no update available)
Ok, deleting the .exd-files works for a moment. This is a temporary work around. MS doesn't has a real solution, but recompiling the code 'solves' the problem.
That is why some people said: 'Add a comment and the problem is solved'. Yes, adding a comment forces a recompilation.
I agree, this is still a work-around, but not a temporary work around. So: 1. check in which part of the VBA-code the error exists 2. add a comment by which a recompile is forced. 3. save the project again
that's all