APEX

Hi all,
I am trying to implement VPD functionality in an APEX application. I use LDAP authentification for authenticating users.
I followed the steps of the tutorial about VPD in APEX http://www.oracle.com/technology/pub/notes/technote_htmldb_vpd.html
My user_only function looks like this:

CREATE OR REPLACE
FUNCTION USER_ONLY
(p_schema IN VARCHAR2 DEFAULT NULL,
p_object IN VARCHAR2 DEFAULT NULL)
RETURN VARCHAR2
AS
BEGIN
RETURN 'upper(partners_bpd.teamid) = upper(teams_bpd.id) and
upper(mn_contact_team.teamid) = upper(teams_bpd.id) and
upper(mn_contact_team.contactid) = upper(contact_bpd.id) and
upper(contact_bpd.username) = :APP_USER';
END;

The trace file reports the following error:

ORA-00904: "CONTACT_BPD"."USERNAME": ungültiger Bezeichner
For those who do not speak german: ungültiger Bezeichner = invalid identifier

Username exists in contact_BPD and is spelled correctly.

Any Ideas?


Tino