For some idiotic reason, I found out that when using Firefox, and I had to re-login to Gmail...which uses the same username as adsense...but a different password...FF decides to replace the Adsense password with the Gmail pwd. This causes a failed login and re-direct to the page that tells you to signup for Adsense. This is basically if you're storing passwords and thinking you're inserting the right one, but actually it's the wrong pwd. Make certain on your actual password for Adsense and avoid going down the change password path...it's a hassle.