owner cant delete from table, permission denied

[Nico Latzer <nico(dot)latzer(at)r-kom(dot)de>]

if i try to delete a row from table "customer", it is not permitted
with msg "customer_discount: permission denied", which has foreign key to customer set ON DELETE NO ACTION

- even as the owner of the tables/database owner
- even when all triggers and rules removed on customer_discount

but i am able to delete a row from customer_discount with the same priviliges kept unchanged,

EXPLAIN DELETE FROM customer works,
EXPLAIN ANALYZE DELETE FROM customer fires "customer_discount: permission denied" again 
 
Please can You give me any hint, in which
direction to look for.
IMO, pg_depend (old dependencies) couldnt be the reason, because theres no DROP involved
REINDEX customer* already done without problems, same with VACUUm
  
postgresql-7.3.2 , data was slurped in from 7.2 few months ago

Thanks for Your efforts,
-- Nico