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