One possible cause for this error is if the Domain Controller is running on the same server as Microsoft Exchange. Microsoft acknowledges this as a defect and has provided a manual workaround for this issue.
For more information, refer to the Microsoft Knowledge Base. On the Internet, go to the following URL:
This article references ASP.NET 1.1, but the article also applies to ASP.NET 2.0.
Unique identifier (UID) errors might occur in Outlook or Outlook Express when using IMAP
This error can occur when the mail client is open on the desktop at the same time a violation is detected on the server. These warnings can be ignored. Refresh the mailbox. Outlook, Exchange, and Mail Security will continue to function normally.