Connected Users No Name

When I look in User Services on our NT4 server I see 2 connected users that do
not have a name. When I highlight them I can see that they are Administrator
accounts because they are using the same resources as the Administrator user.
Do we have a problem on the server or is this something that is normal? On our
BDC I also had a user that was on twice, once without a name. When I
disconnected the one without a name it also disconnected the one with a name.
This person also told me that they have been having a problem logging on for the
past week. They log on in the morning but cannot see the network so they log
off and then log on again and then they are ok.