AUDITING 2007 Problems

Hi, has anyone come across a case where the exchange 2007 SP2 Auditing is switched on but a particular user doesnt show up in the logs...

ACEEX01\MSExchangeIS\9000 Private\Folder Access Expert  

ACEEX01\MSExchangeIS\9000 Private\Message Access Low

I have excluded certain system accounts from being audited by using the extendedrights option but im not sure why this user will not show up in the logs. any ideas