The Application Sharing Server encountered an error when requesting credentials from the A/V Authentication Service. Cause: ...

The Application Sharing Server encountered an error when requesting credentials from the A/V Authentication Service.

Cause: The Application Sharing Server could not establish secure TLS session with the Microsoft Lync Server 2010 Front End Service.
Resolution:
Check the Microsoft Lync Server 2010 Front End Service is alive and that network connectivity exists.