I just enabled the Solver add-in and when I try to start it, I get a "Compile error in hidden module: SolverCode" error. I have tried looking at all of the Excel Start folders (as suggested by similar errors) but they are empty. I am running Win 7 and Office in 64bit mode.
PS I am uncertain whether it is related but several months ago I tried to install an add-in called PH Stat for a class I was taking. It never seemed to work so I uninstalled it, but ever since, Excel asks me for permission to make changes to the hard drive when I start it, and will not open a file directly (i.e. double clicking an Excel file will cause Excel to open (with the permission warning) but will nor open the target file.