Periodic Loss of Network Drive Connection

I have a Server Running WinServ 2003 Enterprise acting as a File Server,
member to an NT Domain. Has worked fine for nearly a year in this setup.
Over the past 3 months, however, I am finding that about once per month, my
client PCs (mostly W2K and a few XP Pro) are unable to connect to any of the
shares on this one server only. When users log out and log back in, script
fails to map drives to shares on this server. Rebooting the Server fixes the
problem, but about a month later, I am running into the same problem. I have
checked the event viewer on the server and nothing out of the ordinary is
taking place, nor am I running into this problem on any other Windows Server
2003 server containing shares. Anyone run into this before or know of a
patch or fix action? Thanks for your assistance.