On a computer that is running the Microsoft Office Communications Server 2007 R2 Group Chat client, you try to log off or try to shut down the computer. In this situation, the Group Chat client crashes. Additionally, you receive the following error message:
System.NullReferenceException: Object reference not set to an instance of an object.
To fix this problem, install the following cumulative update:
2491979 Description of the update for Office Communications Server 2007 R2 Group Chat client: March, 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.