User account loses network access

W7 pro on a 2k3 network.
The user is the owner has admin access to the servers mapped drives. He doensnt log off or reboot often.  He often loses access to the mapped driives and either has to log  has to log off and back on ot he reboots in order to return access. I dont have this issue with any of the win xp machines, just the one Wind 7 Pro Box.  Is there a seeting somewhere that is timmming out his connection or requiring him to reauth every so often?

thanks
Seaweed