File sharing errors

Win XP SP1 Clients, Win2K SP3 Server. Users create a new file on the server from a mapped drive on XP but then cannot delete the file. It says it’s in use and cannot be deleted. No programs are open, no rogue Word,Excel,etc processes are running, tried rebooting the client machines/server. We can delete the file while logged onto the console on the server with no problems. Just can’t delete the file from the xp machine. Doesn’t happen all the time, it’s sporatic, happens more often than not though. Tried this already Q329170, disabled the GPO’s for digitally signing files on the server.