I'm in the process of changing the interface to include GameContainer in the render() method. It will break existing games. I've put a temporary work around in place for the next week so people dependent on the extension don't get broken. However, if you are using the extension to show your game please add:
to the extension reference so you always get the older version for your game. That is of course unless you'd rather update your code.
Your render methods just need to be updated to the form:
public void render(GameContainer container, Graphics g)
Likewise in game state:
public void render(GameContainer container, StateBasedGame game, Graphics g);