Problem with User Level Access on W98 PC

I have a W98 PC in a mixed W2K and W2003 domain. I have the W98 PC set at
user level access and a list of users that have authority. When I try to
connect to the W98 PC, I get an error message stating "Incorrect password or
unknown user name". This has worked in the past and the problem seemed to
have started when I installed a W2003 server. If I change the access to
share level, roboot, change it back to user level, roboot, it works for a
while but then always goes back to the error within 24 hours. Any help would
be appreciated.