There is a known issue in the OCS 2007 R2 Response Group service.

 The service will not start if you have a SAN certificate assigned to the front end server and the last entry in the SAN list does not match the pool name. One way this can happen is if you ran the OCS Certificate Request wizard and checked that box that says “Automatically included machine name”; this will cause it to put the machine FQDN last in the SAN list, which will cause Response Group startup to fail. 

UPDATE 06/05/09: This problem has been resolved in the following patch - http://support.microsoft.com/kb/967829/ . This patch will also be automatically detected if the OCS server is running Automatic Update.