In the Event ID logs from your Microsoft systems are you getting any of the following:

System error 64 - "The specified network name is no longer available"

System error 53. "The network path was not found"

Event ID 3013 - Description: The redirector has timed out a request to ComputerName.

Event ID 2022 - Description: Server was unable to find a free connection NumberOfTimes times in the last NumberOfSeconds seconds.

Event ID 4, an Event ID 1055, and an Event ID 4322, in addition to Event ID 2022 in the system event log.

"The semaphore timeout period has expired"

http://www.chicagotech.net/troublesh...temerror64.htm