Auto Frame type Problems

On my network the past couple of days the windows 2000 clients that connect to our Novell 3.12 servers have been loosing connection. The fix has been going into the frame type and changing it from Auto to 802.3. We never had this problem before it has always been auto. Nothing on the network has changed to my knowledge and the NT40 users machines are not having any problems. Any suggestions would be greatly appreciated.