Just installed NIS on 3 computers to replace last years expiring one. On one of the computers that at first gave the Norton System Framework has stopped running (and after being shut down for over a day- decided to run OK again) seemed to be up & running fine now- when I go to shut down & everything is closed, I get a message like "others are logged into this computer & by shutting down they will lose data". I've never gotten this before on any of 3 computers & am not set up for networking or anything. What does this mean?