Hi Michael,
Are you getting this error on tableupdate() only when adding records? If so, does it occur after the second record is added? Perhaps your primary key fields are not being updated to the base table. If this is the case the first record that is inserted may be getting a blank (or null) primary key fields and the second record with blank or null primary key fields is attempted to update causing this error due to duplicate key. You might try doing a tableupdate after each record is inserted and requery to see what is or is not being updated.

Just a thought
Elmer