your code should be

BEGIN TRANSACTION
INSERT INTO TABLE1 VALUES(A)
INSERT INTO TABLE2 VALUES(B)

IF NOT TABLEUPDATE(1,.t.,"TABLE1")
llOk = .F.
ENDIF

IF NOT TABLEUPDATE(1,.t.,"TABLE2")
llOk = .F.
ENDIF

IF llOk
END TRANSACTION
ELSE
ROLLBACK
TABLEREVERT(.t., "table1")
TABLEREVERT(.t., "table2")
ENDIF