I have a clustered mailbox setting and one of the nodes can't start the exchange system Attendant or system host. I get the follow from my event logs Event 1005 Unexpected error A local error has occurred. Facility: Win32 ID no: 8007203b Microsoft Exchange System Attendant occurred. Event 2142 Process MSEXCHANGEADTOPOLOGYSERVICE.EXE (PID=4544). Topology discovery failed, error 0x8007077f.

Seems like Exch can discover AD se iff below help http://www.chapleau.info/blog/2006/02/12/63.html Also, run the Exch BPA and test Also run the Cluster validation and check for errors - http://technet.microsoft.com/en-us/library/cc732035(WS.10).aspxSukh

Hi, What's your exchange version? Additionally, please verify that you have defined subnet in your AD site. Best Regards!