Access to your logon server has been denied

Our network servers have just been upgraded from NT to
2003 server in preperation for moving the clients to XP
next year.
However, ever since implementing this, frequently our 98
clients are getting the above error when users try to log
on.
A reboot of the machine resolves the issue.
It only seems to occur after the user has just logged off
the machine but not all the time either.
I have just tried to log on with a wrong password it gave
me the above error put in the correct password still got
the error did not change anything and hit ok and its in
this time.
I really have not got a clue what is going on.
Any ideas?


Chris