You cannot call certain Conference Auto Attendant (CAA) contact objects in a Microsoft Office Communications Server 2007 R2 environment. Additionally, a "SIP/2.0 500 Internal Server Error” error message is logged in the Communicator-uccp.log file.
Note The Communicator-uccp.log file is located under the following folder:
This issue occurs because CAA has to stop all the endpoints and restart the CAA service when a temporary network outage occurs together with a race condition. However, CAA crashes without stopping certain endpoints.
To resolve this problem, install the following update rollup:
2403680 Description of the cumulative update for Office Communications Server 2007 R2, Conferencing Attendant: November 2010
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.