This issue occurs because the dial plan isn't recognized by the Exchange Unified Messaging (UM) routing application in the following conditions:
- The Front End server pool isn't able to forward the call to Exchange UM in Microsoft Lync Server 2013.
- Event error 44005 and 44008 are logged in the Lync Server event log.
- There's a connection issue between the Front End server and the domain controller.
Article ID: 4010078 - Last Review: 18 Jan 2017 - Revision: 10