I'm not sure myself either, but what comes to mind is that you're using a recent version of Java that changed some compatibility with the way it used to work (I know it's never supposed to do that, but the code hasn't changed, so that is all that comes to mind). Try running either the crossplatform version or the one for your specific platform, as the versions apart from the crossplatform one bundle a JRE (Java Runtime Environment) with the game, which should work.