Ok, lets throw this one out there:

l'm running an NT4 server with about 50 nt4/2000 workstations, and occasionally when someone tries to open a shared file on the server, they get messages about that file being in use by someone on the network: and that user does not have the file open. The file is not in use, but people still can't access it. Restarting doesn't help, nor does reopening and closing the file.

l've checked around, and there doesn't seem to be any eay solution/reason for this happenning. Has anyone else seen this, or more importantly, FIXED this?