Clients lose their login after idle time

I am converting a network from Netware NDS to W2K3 with Active Directory. There seems to be a problem, especially with WIN98 clients where the login is lost after an idle time. I can’t seem to find the idle time setting in GPE. At first the clients would be locked out. I disabled the lockouts due to password problems and now they don’t get locked but the user has to log off and back on again. This is unacceptable for my client and I can’t seem to figure out a solution. I loaded the DS 98 clients and thought it was working, but they started doing it again. Any ideas? If the clients keep files open, they seem to stay on, but I’m not sure cause the time period seems to vary.