Although there is a way for me to join after reentering the key, this is quite annoying! I already tried to reenter the key, login, go back to Singlelplayer and back again to Multiplayer. In this case, I do not have to reenter the key and I can logon immediately. But after exiting the game and restarting it, it starts over again.
Please, Crytek, have a look at this and let us know if there is any workaround or if you need to apply another patch.