Hi Kevin

>SELECT Table1
>SCAN
>REPLACE Field1 WITH FieldValue IN Table1
>    IF SEEK(Field2, "Table2", 2)
>          IF Table2.Field1 = .T.
>               INSERT INTO Table3 blah blah blah.....
>          ENDIF
>    ENDIF
>ENDSCAN

Are you by any chance using tablebuffering on Table3 ? Or using transactions ?
If so, try to run this without tablebuffering and transactions.

Walter,