Oracle Forms

Hi
I had tied to display alert message in the form..

But it shows FRM-41039: Invalid alert ID 0 - my alert is not displayed ..

The below is my function..

FUNCTION ALERT_SHOW(message VARCHAR2,showmsg VARCHAR2)
RETURN NUMBER IS alert_no NUMBER;
BEGIN
Set_Alert_Property(message,ALERT_MESSAGE_TEXT,showmsg);
alert_no:= show_alert(message);
RETURN alert_no;
END;

The trigger code is as follows..

DECLARE
ALERT_ID NUMBER;
BEGIN
ALERT_ID:=ALERT_SHOW('ERROR','hai');
raise form_trigger_failure;
END;

Thanks