Error message with a SQL function

Hi

I try to create the following SQL function:

CREATE FUNCTION update_affiliate(int,double precision,double
precision) RETURNS void AS ' UPDATE affiliate SET balance=balance +
$2, balance_in_points=balance_in_points + ( $2 / $3 ) WHERE id = $1; '
LANGUAGE 'sql';

but when I submit this query directly with PostgreSQL, I have the
following error message:

PostgreSQL said: ERROR: Unable to locate type oid 325664 in catalog

I think the problem comes from the first parameter ($1) but I don't
understand because affiliate.id is indeed the primary key of the table
affiliate.

Has anybody an idea ?
Thanks
Krystoffff