arcade help

[HS2005]

dear members, i have installed some games but they don not work properly because of i think a table prefix.
when i click

http://forum.groundzero.nu/admincp/hexxagon.game.php

i get this error:

Fatal error: Call to a member function query() on a non-object in /var/www/forum/admincp/hexxagon.game.php on line 20

Line in php file:
$gameexists = $DB_site->query("SELECT * FROM " . TABLE_PREFIX . "games WHERE shortname='hexxagon'");

Kind Regards for a soltuion and how to set the right games in the right section