Chat channels become unavailable in Office Communications Server 2007 R2 Group Chat client

Symptoms

Chat channels in Microsoft Office Communications Server 2007 R2 Group Chat client become unavailable.

Cause

This problem is caused by SQL deadlocks that occur on Office Communications Server 2007 R2.

Resolution

To fix this problem, apply the following update:
979857 Description of the update package for Office Communications Server 2007 R2: April, 2010

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.