If you back up your file using the Backup button at the top right corner, you will have everything you need to restore your business. For this purpose, you can back it up to your desktop. (Normally, of course, you will back up to a separate location. Not a bad idea to make two backups before doing what I’m going to tell you next.)
If you have any other businesses, back them up separately. (Backup only does the current business.)
After backing up, locate the application data folder shown under Application Data under About Manager. Trash the entire folder, not just its contents. Reinstall Manager, but this time, don’t drag anything out of your Applications folder first like you did last time. Follow the instructions in the Guide for updating I sent you earlier: just drag the Manager icon from the expanded disk image into Applications.
Launch Manager and restore the business using the Add Business button. Let me know if that fixes the problem.