Exchange 2007 UM - Can’t get to voice mail

I just resolved an issue where the OCS Front-End and the Exchange 2007 UM server wouldn’t talk with each other. Communicator or Phone Experience would not connect to Exchange UM.

Here is a debug from Phone Experience dialing Voice Mail…

Result-Code: 0xc3e93f30 SIPPROXY_E_INVALID_EDGE_PROXY_HEADER
…and…
SIP 480…
ms-diagnostics: 15007;reason=”UM server did not respond to request”;source=”OCS001.company.net”;dialplan=”Test.company.net”;
umserver=”ex07.company.net”;appName=”ExumRouting”

The Exchange server would produce this event, ID1088:

The IP gateway or IP-PBX “pool.company.net” did not respond to a SIP OPTIONS request from the Unified Messaging server. The error code that was returned is “400″ and the error text is “Malformed Edge Proxy header:The requested operation failed.”.

The OCS server would produce this event, ID44022:

An attempt to route to an Exchange UM server failed.
The attempt failed with response code (Timeout): ex07.company.net.
Failure occurrences: 1, since 4/17/2008 2:34:57 PM.
Resolution:
Check this server is correctly configured to point to the appropriate Exchange UM server. Also check whether the Exchange UM server is up and whether it in turn is also properly configured.

Every Internet search related to Malformed Edge Proxy pulled up certificate related issues. I checked the certificates, but everything looked fine. It wasn’t until I noticed the EventID:1112 showing which certificate the UM service was using did I correlate the issue. This event specifies the specific certificate used by UM. In this case, I compared the certificate assigned to the Default Web Site on Exchange to the certificate used by UM and found differing serial numbers:

I then deleted the certificate used by the UM service and restarted the UM Service and all was well.