To remove invalid or expired certificates from a user:
- Open Active Directory Users and Computers.
- Click View, and make sure that Advanced Features is selected.
- Locate the user in question, right-click, and then click Properties.
- Click the Published Certificates tab. This shows a list of X.509 certificates published for this user.
- Remove any unnecessary certificates.
- Click OK and close Active Directory Users and Computers.
From a newsgroup post: "This is a new feature in Exchange2003 that filters invalid or expired certificates from the Offline Address Book (OAB) generation, thus making the OAB smaller. This effectively translates to lower bandwidth requirements for the Outlook client when it downloads the OAB. In most situations this is nothing to worry about".
Within AD Users and Computers navigate to the "Published Certificates" tab for the userís account listed in the warning message and remove any invalid or expired certificates.