PROBLEM WITH FUNCTIONS

Hi.

i have a problem with a function.

i create a type unidades  CREATE TYPE unidades AS (codigo numeric(3,0),                           descripcion text);

and i create a function get_unidades   CREATE FUNCTION get_unidades(int4, int4, int4, int4) RETURNS  typeof
unidades AS '
SELECT cucoduni, cudesuni
FROM cumauni
WHERE cuempuni = $1 and     cuseduni = $2 and     cucaruni = $3 and     cuasiuni= $4
; '  LANGUAGE 'sql';

and at this moment´s it´s all ok BUT when execute this function    select get_unidades(10,1,15,17)

say    "cannot display a value of type RECORD"

any idea, PLEASE HELP MY

saludos