Article ID: 973337
This article applies to the following product:
When a peer-to-peer file transfer is performed between two Microsoft Office Communications Server 2007 R2 Group Chat clients and one or both clients are behind a firewall, the transfer fails.
This problem occurs because the Group Chat client that is behind a firewall provides an incorrect IP address to the other client. Therefore, the other client times out when it tries to make the connection.
To resolve this problem, apply the following update:
(http://support.microsoft.com/kb/969818/ )Description of the update for Microsoft Office Communications Server 2007 R2, Group Chat Client: July 2009
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.