My Exchange is 2007 running Windows 2003. I just tried to access OWA and got this error message
Outlook Web Access could not find a mailbox for LOCALDOMAIN\IUSR_MAILSER. If the problem continues, contact technical support for your organization and tell them the following: The mailbox may be stored on a Microsoft Exchange 2000 or Microsoft Exchange 2003 server, or the Active Directory user account was created recently and has not yet replicated to the Active Directory site where this Client Access server is hosted.
What caused the problem