I would love for the problem to be fixed - I only offer suggestions that have worked for me and therefore they are worth at least trying.
Try logging out of the game (via the frontpage logout option) and make sure you log out of here too (via the logout option).
Close the browser.
Re-open the browser and log in. Do not try to change worlds!
Try the play now button, even if it is on a wrong world. Use the in-game world changer.
If all this works, then you're in! If not, then ...... hopefully they will eventually clear this up completely!