We recently replaced our global catalog server with new hardware. The new gc was brought up, designated as a gc in Sites and Services and we then waited for several days to allow for replication to complete. The old gc was then removed from the forest via dcpromo after we confirmed and tested that the new gc was operating and there were no replication errors related to the old gc. On our Exchange 2007 servers (mailbox role), we receive the following warning message in the application log: Source: MSExchange ADAccess Category: Configuration Event ID: 2091 Description: Process MSEXCHANGEADTOPOLOGYSERVICE.EXE (PID=1212). The domain controller specified in the registry (<name of old gc>)was not found in the Sites container in Active Directory. Exchange Active Directory Provider will not use this server as a domain controller or global catalog. I'm not sure where this is set and how to configure it to reference the new global catalog server. As far as functionality is concerned, I can't see that this is affecting anything, just trying to clear up the event log at this point (and it makes me a bit nervous).