Returning SETOF INTEGER mystery...

Hello again, i found ou that no matter the function, if the return type is a
SETOF INTEGER, or a SETOF CUSTOMTYPE that includes at least ONE INTEGER
value, the error:

WARNING: plpgsql: ERROR during compile of buscarseccion near line 6
ERROR: missing .. at end of SQL expression

Shows up, is this a bug or am i doing something wrong?

Here goes another function that throws the same error ( I have plenty in
case you want to see them)

CREATE OR REPLACE FUNCTION BUSCarSeccion(VARCHAR) RETURNS SETOF
BusCarSeccion AS '

DECLARE
Libro ALIAS FOR $1;
res BusCarSeccion;
BEGIN
FOR res IN select alto,altoIntercita, espacioCabeza, EspacioFin,
idColor, idColorTexto from CARSeccion where IdLibro =
Libro LOOP
RETURN NEXT res;
END LOOP;
return;
END;

' LANGUAGE 'plpgsql';

JuanF
(a newbie with MANY questions)