You can configure the AutoDisconnect time by running the following command from a command prompt:
net config server /autodisconnect:time_before_autodisconnect
Specify the time in minutes.
http://support.microsoft.com/kb/314882
Or, I found this:
I had the same problems (Dropped drives, workstations disconnecting, ect.) and could not find a solution anywhere. But I finally did find an answer. Try one of the following or both:
[To turn Autodisconnect off] Type > net config server /autodisconnect:-1
[Try this on the server and ws]or
Install or repair the DHCP, DNS and WINS on the server. Setting up theses services “correctly” Completely! solved the problem. I did them all at once so I am not sure which one was the trick but I suspect WINS was the key.