Article ID: 978369 - View products that this article applies to.
If the network disconnects and then reconnects, the Microsoft Office Communications Server 2007 R2 front-end server that you connect to changes. Therefore, instant messaging fails.
To fix this problem, apply the following update:
(http://support.microsoft.com/kb/977345/ )Description of cumulative update for Office Communications Server 2007 R2: January, 2010