Better solution posted here (no offense to Brad):
"Backup data. Uninstall. Install to C:\Users\YourUserName . Problem (should be) solved.
That eventually happened to me on Vista, I looked at some fixes and everything, this worked like a charm and it never happened again. When I installed Win7 I installed to Program Files and shortly after it happened again, so I did what I said, problem solved again."
Since installed to this directory, the glitch has never happened to me.