Fail to disable the Simultanous-use, somebody help me.

[Alexandre Chapellon]

I don't your problem have anything to deal with simultaneous-use checking... Indeed, when enabled Sim-Use would REJECT NEW users trying to connect to if the login used has reached the limit.... What you say is that new user (same login) disconnect existing session... This sounds more like something with netscreen for me...eg could be ip allocation pb if managed by netscreen or something like this...
May be providing debug of query processing would be more usefull than just the startup.