ERROR: UNIQUE constraint matching given keys for referenced table "sequences" not found

I'm trying to create some tables with foreign keys.
When I try to create a foreign key ...
   foreign key(seq_code) references sequences(seq_code) on update 
CASCADE on delete CASCADE,

I get this message:
   ERROR:  UNIQUE constraint matching given keys for referenced table 
"sequences" not found

The problem is that the referenced field and table exist.
Any hint?

Using psql and PostgreSQL 7.1.1 on RedHat 7.1
Thanks.

-- 
Dado Feigenblatt                                 Wild Brain, Inc.   
Technical Director                               (415) 553-8000 x???
dado@wildbrain.com                               San Francisco, CA.