Seb I see you were able to help some people out with the dreaded 999 error. It seems it's struck again with me. I read that some people tied this error with having a friend that was banned. This the case with me as well.. my brother was forced to change his online id but I was just his friend and not clan mate. Sony changed his name and he is back and playing killzone 2 just fine, myself, I'm getting the 'account already exists' 999 error.
Anything you can suggest? I contacted sony and they refuse to change my online ID because this is a game related problem, not psn network problem.