Here's a list of recently released fixes for OCS 2007 R2 Group Chat 

Office Communications Server 2007 R2, Group Chat Server

http://support.microsoft.com/kb/980042

Office Communications Server 2007 R2, Group Chat Client

http://support.microsoft.com/kb/980043

Office Communications Server 2007 R2, Group Chat Admin Tool

http://support.microsoft.com/kb/982128

Office Communications Server 2007 R2, Group Chat Server SDK

http://support.microsoft.com/kb/981449