Unable to play multiplayer

That is the servers plugin, when you first join the server you have to register/sign up. (don't use your real password!)

This isn't something that the bug tracker can assist with. If you can't pass the server's security features, please contact them as the team cannot help you here.

Thanks alot, that was helpful 

I added the password as suggested but it works for a few minutes then it kicks me out

Yup, this is a server issue in that case. Please approach the server's owners for assistance.