Ok so there's a quest in Droughtlands that is repeatable and given by a Centaur. He offers to turn you into a centaur and you go on a race. I grabbed the quest but wasn't really paying attention and failed it.
Here's the catch - if you fail this quest and don't abandon it you cannot login on that character again, the client will crash to the desktop. Thread Here
So, yeah. I can't log in my main character. I have petitioned but apparently I have to phone them.
Don't do this quest. It's not hard but the penalty for failure is a bit extreme.