Corrupt NT user profiles.

My school district is experiencing the corruption of user account roaming profiles. We have ~1700 workstations on our NT4 network with ~8000 accounts. The server where our user accounts reside is a Dell PowerEdge 2300 with dual processors and connectedto a Cisco Catalist 5500 switch. The ntuser.dat file seems to be getting truncated when the user logs off and the system is trying to copy the roaming profile back up to the server. WHAT MIGHT BE CAUSING THIS AND WHAT CAN I DO TO STOP IT FROM CONTINUING TO HAPPEN?