ORA-01422 due to Logon Trigger

Below is the code of the trigger used, which is causing frequent "ORA-01422: exact fetch returns more than requested number of rows"  errors. My guess was the audsid 0, which is for Background processes but even after excluding it, I still get the errors!! Need some urgent help on this.

CREATE OR REPLACE TRIGGER XX_APPS_RESTRICT_TOOL
AFTER LOGON ON DATABASE
DECLARE
L_TOOL V$SESSION.PROGRAM%TYPE;
L_DB_USER V$SESSION.USERNAME%TYPE;
L_OS_USER V$SESSION.OSUSER%TYPE;
L_SID V$SESSION.SID%TYPE;
L_SERIAL V$SESSION.SERIAL#%TYPE;
BEGIN
SELECT PROGRAM,USERNAME,OSUSER,SID,SERIAL#