Shafid,

You can use a record lock to insure the barcode number is not duplicated. Example code is below (untested just use as an example).

LOCAL lnBarc
SELECT barcno   && table with barcode number
IF Barcno <= 0
   MESSAGEBOX("This computer is not setup with barcode numbers","")
   RETURN
ENDIF 	
DO WHILE NOT RLOCK()
ENDDO
lnBarc = Barcno.Barcno  
REPLACE Barcno WITH Barcno+1  &&increase by one
UNLOCK