You may have to play through the intro/tutorial, then you'll be able to log into other accounts. I've had this happen when I removed then reinstalled the app.
I had that screen come up last week when trying to login at the backend of a server update. Happened a couple of times in a row, so left it for 15 mins then tried again and all was fine.
whats wrong with the game, been tryin to get in for 24 hours no f...in luck. all i get is "update available" update to continue playing, press the update button, and nothing F&%$in happens. can u give me a reason?????