I have an intense VBA "macro" that has a user form and gathers a bunch of data from the user, then manipulates and saves the data (using INI files) then opens a Viewer spreadsheet and allows the user to export the final reports to yet another Excel spreadsheet (removing the overhead of the VBA code).

Suddenly in development the main program causes a "fatal error" and shuts down Excel. If I re-open and DISABLE macros and save and reopen - it works. If I compile and save and open it crashes.

Interestingly the Viewer does the opposite it crashes if I don't compile and works if I do.

My question is what exactly does compiling do that appears to wreak havoc on these two files?