Do you guys have the correct realmlists, double check your config files.
I really can't think of more reasons, this topic was made when mop was released quite a while ago, and I haven't played MoP ever since the meltdown. You can always try to download a fresh copy of config files, you can delete everything except the core files which don't change, and download only small files like configs, settings and such.
Also never use email to login to the server, if you perhaps used email, you will have to get a new client again.