The A/V Authentication Service returned invalid response. Connections that require Firewall traversal will not be successful. ...

The A/V Authentication Service returned invalid response. Connections that require Firewall traversal will not be successful.

Response Code: %1
Response Text: %2

Cause: Either the A/V Authentication Service is not running or unreachable.
Resolution:
Verify that A/V Authentication Service is reachable from the computer running Lync Server. The response text may also indicate a configuration issue.