Communications Server 2007 R2 front-end server does not recognize a 504 error message that is sent by Communications Server 2007 R2 Mediation Server after you install update 956829

You install update 956829 on a Microsoft Office Communications Server 2007 R2 Mediation Server. Mediation Server sends a 504 error message to the Communications Server 2007 R2 front-end server when a PSTN gateway is unreachable because of connectivity issues. However, the Communications Server 2007 R2 front-end server does not recognize the format of the message and marks it as BAD MESSAGE FORMAT. Therefore, the failover recovery mechanism is affected. The time before the call is rerouted to another Communications Server 2007 R2 Mediation Server and PSTN gateway increases from 20-30 seconds to three minutes.

The wait time for end-users to be routed to another Communications Server 2007 R2 Mediation or PSTN gateway increases from 20-30 seconds to 3 minutes.

To resolve this issue, apply the following update: After you install this update, Communications Server 2007 R2 Mediation Server sends a 504 message to the Communications Server 2007 R2 front-end server. The message is recognized by the Communications Server 2007 R2 front-end server.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.