I am having a problem with a new Windows 2008 file server. The problem is when you try to access a mapped network drive, they are not reachable. Even navigating to \\fileserver, doesn't work. It says it cannot be found. I had this problem earlier only with users using Windows Vista. I rebooted the server and everything came up OK and users were able to get their data. A few hours later the same thing happened but only to Windows XP users. I just rebooted and everyone can get in again.
I have disabled the firewall.
Disabled Symantec Antivirus Corporate.
Nothing else is installed.