I've just tested my own code, and it's working fine, i've got it running on my forum now -
http://gamevine.co.uk/forum/tetris.php and i've just had one of my users help me test it by changing his usergroup to each of the available ones, and he was denied access on all the ones I did not want him to have access with.
please feel free to make the changes I have suggested, esp if you are using a foregn board, but as i said before, make sure you BACKUP tetris.php before making the changes