Well... I would say good job but I tested it and it gets no errors but...
I tried this I loaded 2 clients logged in on my acc then tried logging in on the other client with the same acc and It just kicked my other acc.
But then if someone found out another players password and wanted to steal there items they would easily be able to then because all they would have to do is try and log in and it will kick the player and then they are in..