I agree with Padi that it's probably a log in loop. I am struggling with it on Chrome at the moment, despite taking the steps that Padi mentioned, numerous times.

Another thing to consider is, you can't change your email address to resemble your username. If your username is say pink-pig, you can't change your email to pink-pig@yourisp.com.

I think it's a log in loop though, so do what Padi said.