Robert,
I usually encounter this fatal error message when a dbf or scx file is corrupted.
Tell tale signs are that when u use the suspected table (or scx), try to append a record. If the file is corrupted, u get the fatal error straight away.
To resolve it, modi stru, change one of the field or add a new field, save it, modi stru to change back, then run a pack after that.
HTH
Yau