In my case, this error was caused by the Mac Power settings dropping the connection. On Mac OS X, go to Energy Saver in the System Preferences. You may need to click Show Details to show all the settings. Under Sleep, set the system to “never sleep”.
From a newsgroup post: "I had the same problem. It turned out to be a faulty Ethernet switch/hub. Our NT workstations were getting disconnected as well as our Macs, but this was harder to spot as NT reconnects in the background. As soon as we replaced the switch, everything was Ok. Therefore, my advice is to check out the infrastructure of your LAN: cabling, hubs, switches, etc".
See the link to "EventID 12061 from source MacFile" for additional information on this event.
Check to see that the Netlogon service is running. After a server reboot, the Netlogon service terminated unexpectedly with EventID 7024 logged a couple days prior. Windows users could access files on the server, but Mac users could not.
Trying to automount Mac User home folders through netinfo (mac osx)on Win2k server afp shares. Appears to be some domain security setting that's causing the problem.