A failure occurred while trying to contact the Mailbox server '%1' for the '%2' operation. Please make sure that the Microsoft ...

A failure occurred while trying to contact the Mailbox server '%1' for the '%2' operation. 
Please make sure that the Microsoft Exchange Unified Messaging service is running on the target server, and that the server is part of the subscriber's dial plan. The user on whose behalf the operation was initiated: '%3'. More information: '%4'.