Actually there is a bug playing up with email accounts. I have checked on Google yesterday; looks like many users are having that problem. It keeps asking you over and over for your password, though the password is correct as it is working on the Yahoo site on the phone. I have tried all the tips and tricks found on Google yesterday, I have been trying at least 20 times until my eyes were so sore that I gave up. Today this morning, I gave it a try and magically it works. So there is a bug doing that in iOS6 which Apple should iron out.