Problem with plpgsql installation!!!

Hi, I have a problem installing "plpgsql" in postgreSQL 7.4.6 on linux.
Those Scripts were create succesfull but when i try to create some "store
procedure(function)" no gererate errors, no generate nothing in the pgadmin
III, i don't know what is the problem.

'/usr/lib/postgresql/plpgsql.so' exist!!

those are the script:

CREATE FUNCTION public.plpgsql_call_handler () RETURNS language_handler AS
'/usr/lib/postgresql/plpgsql.so' LANGUAGE 'C' VOLATILE;

CREATE TRUSTED PROCEDURAL LANGUAGE 'plpgsql'
HANDLER public.plpgsql_call_handler;

help me please.

thanks.