User Disconnection

This has frustrated me for the longest time..ok two weeks. I have a user who walks away from his/her (win98 se/ novell client 3.3) workstation for 10+ minutes and return to find that have been logged off. On the server, the watchdog packets are set to 10 packets sent every 1 minute and the first is sent only after 5 minutes of no activity. I have increased to maximum time possible but still occures. Why is this happening? And why is this happening to only one user out of one hundred users? Can anyone help. Thanks