Some players report that they have not been able to log in to the game, and that it encountered after the guild update with the new ranks and functionalities. This is due to some bug with the guild interface. Right now there is only one solution for the problem:
Download the German client, install it, log into your account and leave the buggy guild. After that you can return to your normal client and play as usual.
Thought I'd put that up here, in case anyone is affected or someone is browsing the web for help.