pk-fk delete problens

Hallo,
table A
x : int, increment, identity, index
relationship: fk_b_a has pk in A:X , fk in B:X
enforce for repl , insert i update-selected
Table B
x : int, index
relationship: fk_b_a has pk in A:X , fk in B:X
enforce for repl , insert i update-selected
relationship name in B is marked with infinity symbol.
Cant remove record from A, bacause
DELETE statement conflicted with COLUMN REFERENCE constraint 'FK_B_A'.
The conflict occurred in database 'xxx''.
Relevant record from B is removed properly.
CREATE procedure deleteAB(@.ser int,@.rv int output)
as
begin
delete from A where x=@.ser
delete from B where x=@.ser
set @.rv=0
end
what is wrong ?
Tia
pluton> delete from A where x=@.ser
> delete from B where x=@.ser
Its ok, order
pluton