possible consistency problem

Hi,

some days ago I removed all foreign keys from the database to speed up
an import.

Now I tried to create the keys again but it says:

ALTER TABLE ONLY xxxxxxx ADD CONSTRAINT yyyyyyyyy FOREIGN KEY (zzzzzz)
REFERENCES aaaaaaa(bbbbbb) ON UPDATE CASCADE;
ERROR: constraint "yyyyyyyyyyy" for relation "xxxxxxxx" already
exists, but it's not in the schema

when I do:
alter table only payments drop constraint yyyyyyyyy;

it says :
ERROR: "cccccccccccc" is an index

note: the constraint in the error message in differed from the
constraint in my drop statement !!! (I tried to drop the foreign key
but in the error message it speaks of the primary key)

what is this ?

Thank you and Kind Regards
Sebastian