Do not regenerate session_id

[eluser]Agustín Villalba[/eluser]
Hey gyo! That solution is a great solution... but that's not exactly good for my problem, beacuse I need that when a user enters in my application, his username and pass have to be locked. So, if another person tries to log-in with that username and password, the system must say "Hey, there's another guy in the system with this username right now".
So, your solution is great, but I can't allow that a user ejects another user logged-in right now. I need to lock a username if someone logs-in with it and don't allow another person use it to enter in the system.
Anyway, thanks a lot every one who has tried to find a solution to this problem in this topic. Thanks to every one!