Why is the automatic nickname completion facility in Microsoft Outlook finding the wrong information?

Answer

Outlook maintains an internal cache for the purposes of the automatic nickname facility. If the details for that nickname change within the GMS database Outlook will be unaware of this, thus allowing the client and the underlying database to get out of synchronization.

Microsoft acknowledges that this cache may get out of synchronization or become corrupted from time to time. The following link provides details of how you may resolve the issue – http://support.microsoft.com/?kbid=287623