When the presence load is heavy and the rate of requests for polling subscription is very high, Microsoft Office Communications Server 2007 R2 and Microsoft SQL Server report frequent SQL deadlocks. Additionally, requests from Office Communications Server that are queued in the database are dropped. Note If lots of group chat clients are deployed, this problem is more likely to occur. This is because this topology has frequent requests for polling subscription.
This problem is caused by an SQL deadlock in the RtcBatchQueryCategories stored procedure.
To fix this problem, apply the following update:
979857 Description of the Office Communications Server 2007 R2 update
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.