When Microsoft Lync 2010 users try to host or join an Audio/Video conference, the operation does not work. This problem continues until the Audio/Video Conferencing service is restarted. Additionally, the following event is logged in the Application log on a Lync Server 2010, Conferencing Server computer:
This issue occurs because daylight saving time (DST) sets the time back an hour. Certain operations are not configured to process during this time frame, and this causes time-outs to occur.
To resolve this issue, install the following cumulative update:
2514975 Description of the cumulative update for Lync Server 2010, Conferencing server: April 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.