When Spotlight on Messaging runs an internal OWA Health Test Event ID 2070 is triggered on the CAS server with the following description:
Process w3wp.exe () (PID=6132). Exchange Active Directory Provider lost contact with domain controller Server.Domain.Local. Error was 0x55 (Timeout) (Active directory response: The operation was aborted because the client side timeout limit was exceeded. ). Exchange Active Directory Provider will attempt to reconnect with this domain controller when it is reachable.
This can be caused by Network or DNS errors causing the Exchange Server to loose connectivity with the Active Directory Global Catelog server referenced in the error message.
It is recommended to ensure that no DNS entries exist for Global Catelog servers that have been retired, and verify network connectivity between the exchange server and Global Catelog servers.
As this issue may have farther reaching impact to the exchange environment it would be recommended to contact Microsoft for further asstance troubleshooting these events.
Further information about this error can be found in the following Microsoft Technet Article:
