I did log out in single-player mode and it seems to be an issue:
"Log out in Single Player instance for more than 4 hours blocks character
Some players, who logged out their character for more than four hours in a single player instance could not log in with that character afterwards. We are aware of the issue and are working on a fix.
In the meantime please do not log out while being in a single player instance. You know when you enter such an instance when you get the message that the playfield you now go to is for your character only."