KB Article: http://support.microsoft.com/kb/2527360

INTRODUCTION

Consider the following scenario in Microsoft Office Communicator 2007 R2:

• The Office Communications Server 2007 R2 front-end servers for the pool are taken offline.
• The Office Communicator 2007 R2 users in the offline pool are moved to a secondary pool to make sure of their instant message and conferencing functionality.

In this scenario, the Office Communicator 2007 R2 client does not update the EndpointConfiguration.cache file by using the correct pool FQDN and TCP port information.

Additionally, the automatic sign-in process for the Office Communicator 2007 R2 users who were moved to the secondary pool is slower than usual in any one of the following situations in Office Communicator 2007 R2:

• During an initial Office Communicator 2007 R2 automatic sign-in after the user is moved to the secondary Office Communications Server 2007 R2 pool
• During an Office Communicator 2007 R2 automatic sign-in after you exit the client application for an extended period.
• During an Office Communicator 2007 R2 automatic sign-in after you restart the Windows client-based computer on which the Office Communicator 2007 R2 client is installed.