@Isabel - welcome to MobileRead.
I'm afraid any authorization issues you should take up with Goodreads, there isn't anything I can do about it. It does happen that from time to time their authorization service is down or has issues, or it could be a problem with your account. Any time there has been problems with this in the past (if you look back through the thread) it has been resolved by Goodreads at some point. Try their help desk and see how you get on...