Allright, I worked it out and got on Kar'tai server. The trick here is when it popped up the "Invalid game folder" error message, get on the server again, it will work and you'll be in.
Best thing to do is to try and uninstall/reinstall the game. If that doesn't work then rename the main JA folder and reinstall the game, then migrate (move) your maps and other files you installed from the old folder into the new folder.
Ok then that is cool i never had that problem