1] Font Cache Corruption Could be the cause - there are a few utilities that will clear System Caches, System Font Caches, User Font Caches and some will clear Application Font Caches. AppleJack would be my first suggestion. Font Xplorer (if the free version was still available) would be second. Onyx is a good choice, there are others. CCleaner for Mac is newish, I have tested it, but not extensively. Leopard Cache Cleaner is an option.
2] Preference corruption in a seemingly unrelated system or utility or app IS possible, but unlikely. Log into the problem user Move the contents of the User's Library Preference folder to another New Folder.
Immediately Restart in Safe Mode - Login to problem user. Test.
Do you know that FMP 8 will not work on Lion or above? Also that FMP 8 is no longer serviced by FileMaker Inc.
You may have to re-install MacOS 10.6.0 without updates or go to FMP 11 or 12. FMP 11 works with FMP 8 directly.
I am currently moving and testing FMP 8 => FMP 11 [ Note: not required ] but i want to use some new FMP 12 capabilities while assuring all Windows and MacOS users a smooth operation before the leap to FMP12 changes we are doing.