Article ID: 2884793 - View products that this article applies to.
Consider the following scenario:
To resolve this issue, install the following cumulative update:
(http://support.microsoft.com/kb/2884623/ )Description of the cumulative update for Lync Server 2010, Group Chat: October 2013
This issue occurs because of an exception that occurs when Active Directory parses the changes of the DG.
Note Users who are parsed before the exception occurs will have access to the Group Chat room.
For more information about a similar issue, go to User cannot join a Group Chat room after you add the user to a DG that is a member of the Group Chat room in a Lync Server 2010 environment