For most users an error that can't be rebuilt means you've got bad data corruption - no choice but to restore the last backup and reenter the lost data, or pay QB to try to fix it.
But for a QB mechanic, you can open the hood and try to find and fix the problem yourself.
The hood latch is at F2 - F3 and the first place to look is in the QBWIN.LOG file - it will contain more detailed info on the problem which you might be able to use to fix it manually. The only way I have successfully fixed a problem is to remove the broken parts (QB entries) and replace them with new one (reentrer) - I have never found editing damaged entries to work.
Above is for a windows based system - I don't know what the MAC equivalent is.
