Oracle Log on/Log off tracking

Hi, I found another experts exchange topic that directed me to this website: http://www.dba-oracle.com/art_builder_sec_audit.htm  to create a custom user log on / log off table in the database.  I thought this was really neat and wanted to use it.

I was able to get the log on trigger created and it works... however, I can't get the log off trigger to work.  

Whenever I try to execute the code to save the trigger it says:
8/35    PL/SQL: ORA-00942: table or view does not exist
5/1     PL/SQL: SQL Statement ignored

And it highlights this part of the code:
BEFORE LOGOFF ON DATABASE

I am running Oracle 11g ... did they remove this key word?  I have verified that my actual table names within the procedure are correct.  Attached is the code I'm trying to execute.

create or replace trigger
   logoff_audit_trigger
BEFORE LOGOFF ON DATABASE
BEGIN
-- ***************************************************
-- Update the last action accessed
-- ***************************************************
update
PAYROLL.SYSTEM_USER_LOG
set
last_action = (select action from v$session where     
sys_context('USERENV','SESSIONID') = audsid)
where
sys_context('USERENV','SESSIONID') = session_id;
--***************************************************
-- Update the last program accessed
-- ***************************************************
update
payroll.system_user_log
set
last_program = (select program from v$session where     
sys_context('USERENV','SESSIONID') = audsid)
where
sys_context('USERENV','SESSIONID') = session_id;
-- ***************************************************
-- Update the last module accessed
-- ***************************************************
update
payroll.system_user_log
set
last_module = (select module from v$session where     
sys_context('USERENV','SESSIONID') = audsid)
where
sys_context('USERENV','SESSIONID') = session_id;
-- ***************************************************
-- Update the logoff day
-- ***************************************************
update
   payroll.system_user_log
set
   logoff_day = sysdate
where
   sys_context('USERENV','SESSIONID') = session_id;
-- ***************************************************
-- Update the logoff time
-- ***************************************************
update
   payroll.system_user_log
set
   logoff_time = to_char(sysdate, 'hh24:mi:ss')
where
   sys_context('USERENV','SESSIONID') = session_id;
-- ***************************************************
-- Compute the elapsed minutes
-- ***************************************************
update
payroll.system_user_log
set
elapsed_minutes =     
round((logoff_day - logon_day)*1440)
where
sys_context('USERENV','SESSIONID') = session_id;
END;

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