Barbara,
I have seen this error with programs that have timers or methods which switch work areas causing seeks on an unexpecting table.

Its usually wise to always use IN (workarea) in all seeks, replace, etc. Basically if the command supports "IN (workarea)", I would recommend using it, if not, consider seek(), insert into, and any command that keeps you from having to switch work areas (one of VFPs slowest operations).

Hope this helps,
Ed