We are running 4.90 sp2 client on a mixed tree nw 6.5sp2 and 5.1sp8

We are having a random login problem where some staff try to login but
all that happens is the Novell Login "N" appears. Staff can sometimes
login after several reboots.

We have tried setting the prefered server to point at some of our other
servers, turned off NMAS (which we do not require).

The problem seems to come and go and random. Staff have reported being
able to login if they enter there login name and password within a short
period of time after the login box appears, I am not sure if this is just
a co-incident.

This is a recent problem, which is only affect our staff and not our
students, the only difference is that the students use contextless
logins. No changes have been made to the server or clients, this problem
seems to have just appeared.

I have checked the switches to make sure spanning-tree is turned off.