"you're already logged on"

Well this is the seconds time this glitch happened to me. I wanted to check if any of you guys know the causes. From what I know it's from exiting the game by pressing Alt+F4 (so don't :P), leaving the server when its nearly full therefore the system lags and doesn't log you out. Do you guys know any other causes to this glitch?
And if this occurs to you the only way fixing it is waiting for a Server Check, and if you're unlucky two. Anyways I wish you all managed to avoid this glitch (unlike me) and kept Buck being the awesome guild it is <3