Hey backdrop,

More directly to the question. Excel in 2003 saved all files as .xls. Those with macros and those without. When the newer versions came along you needed to save them at .xlsm. Read:
https://superuser.com/questions/7320...ing-excel-file

Perhaps you are opening some newer files that are .xlsm and trying to save them as .xls and the VBA part is lost. This would happen if you had macros in a new file and saved it as .xlsx - the macros would be lost. I have no idea how you might check this theory but it is closer than an OS or Regedit type answer.

I'm just trying to brainstorm on what may be the problem.