Problem with a PL/pgSQL function

I create that function:

CREATE FUNCTION livreEmprunte(int8)
RETURNS varchar AS '
DECLARE
reponse varchar(200);
noDocu alias for $1;
BEGIN
SELECT CASE
WHEN dateremise > date(now()) then
varchar \'Emprunt jusqu\'\'au \'||
substring(datetime_text(now()) from 21 for 4)||
varchar \'-\'||substring(datetime_text(now()) from 5 for 3)||
varchar \'-\'||substring(datetime_text(now()) from 9 for 2)||
varchar \' par \'||nomembre
WHEN dateremise < date(now()) then
nomembre||
varchar \' devait le remettre le \'||
substring(datetime_text(now()) from 21 for 4)||
varchar \'-\'||
substring(datetime_text(now()) from 5 for 3)||
varchar \'-\'||
substring(datetime_text(now()) from 9 for 2)
ELSE varchar \'Disponible\'
END AS disponibilite
INTO reponse
FROM prets
WHERE montantpaye IS NULL AND nodoc = noDocu;

IF NOT FOUND THEN
reponse:=\'Disponible\';
END IF;
RETURN reponse;
END;
' LANGUAGE 'plpgsql';

The function is created correctly, the PL/pgSQL language is installed correctly
and the select works when I execute it directly from psql prompt.

But when I call the function with: "SELECT livreEmprunte(1);", I receive:
ERROR: fmgr_info: function 20288: cache lookup failed

I'm using RedHat Linux 6.0 wth PostgreSQL 6.5.2

What cause my problem?

Thank you.

ric Prvost-Dansereau
e-mail: eric(at)esc(dot)rosemere(dot)qc(dot)ca