Can not connect.

Seriously, what is wrong with this. I have just transfered a character from neltharion to this, downloaded the client from the site, but upon trying to connect, it tells me that I need to register to a battle net account and if I close that window, I enter my password again and it's stuck on connect. I have checked the realmlist and everything is fine there (I downloaded the client from this site, after all). I have never ever had such a problem before with any other clients ... Does anyone know what may be the problem here ? Thanks in advance.