I'm not sure if you're still have this problem, also I'm not sure if what I did to fix it was a coincidence or not. Anyway, I had this exact problem for the last 3 days, I sent a message to google via Contact Us from my gmail account. I described the problem and sent the message. I got back what seemed like an automated reply about knowing about the issue and they're working on it. Then 5 minutes latter I get the gmail notify dialog asking for my username/password and it starts working again. Give it a try if you're still having problems, maybe google's autoresponder is smart enough to pick up the "The page you requested is invaild." and reset something in my account on their end.