Valid Win32 Application

This is my first post so I'm likely to appear stupid. I'm of average computer competence but love the things. Short story is this:I have an accounting program in which I have data files for each year of my business. These have been successfully backed up for years on CD and now JumpDrive, and stored on the desktop with a shortcut for easy access.I downloaded and installed SP2. Now when trying to open a file, I get the message C:XXXXXXXXX is not a valid Win32 application. It always was before so what changed?I cannot back up my current files because that is the name I've always used. The computer doesn't recognize the name as valid so I have no security. An ancillary problem is that years ago, my adorable husband somehow associated my old data file to be opened with MusicMatch. (We don't even discuss this.) I managed a workaround so that I got the files to open with their program application even though I could never change the icon from MusciMatch. No harm no foul. No longer. Post SP2, the danged thing went back to opening MusicMatch, ignoring my old workaround. Messing with it for hours got it to where I'm now getting the invalid file messagel.