ALTER TABLE table DROP CONSTRAINT problem

I have a strange problem on 7.2.1

I am trying to drop a constraint that was set up by this SQL
ALTER TABLE customer_main ADD CONSTRAINT cust_main_agent
FOREIGN KEY ( agent )
REFERENCES customer_main ( id )
NOT DEFERRABLE;

So I do this:
ALTER TABLE customer_main DROP CONSTRAINT cust_main_agent RESTRICT;
And get this error:
ERROR: ALTER TABLE / DROP CONSTRAINT: cust_main_agent does not exist

So I try to violate the constraint and I get this:
ERROR: cust_main_agent referential integrity violation - key referenced from
customer_main not found in customer_main

Any ideas? I am wondering if postgres doesn't like the fact that I have a
constraint going from one column to the id (serial) column of the same table.
--
Lewis Bergman
Texas Communications
4309 Maple St.
Abilene, TX 79602-8044
915-695-6962 ext 115