SELECT so_detail
SCAN FOR so_number = so_header.so_number
<>
ENDSCAN

How about using....

SET ORDER TO so_number IN so_detail
IF SEEK(so_header.so_number,"SO_DETAIL")
   SELECT so_detail
   SCAN REST WHILE so_detail.so_number = so_header.so_number
   <>
   ENDSCAN
ENDIF

also, are the tables local or a shared database that every PC uses?

>You mean changing the value of a field in any index field? I'm not changing the value of the so_number index.