Get the error message that no Domain Account is associated with user.
Also see event viewer error
Gateway: The call to Directory::FindByDomainAndName failed with [0x8004054B] for the NT account: XXX
Gateway: Error [0x8004054B] retrieving mailboxes associated with NT account : XXX
Found one workaround was to restart AvCsGateway and that did not resolve the problem
Unity 3.1(6)
TSP 7.03b
Windows 2K OS
Thanks,
Vince