Well, I can tell you why it doesn't work. The requests being made by miner.gxboxlive.php on line 93 are being rejected.
Code:
$card_string = fetch_file_via_socket($fetch_url . "?bot=gXboxLive_" . $gxblprod['version'] . "&ref=" . $vbulletin->options['bburl'] . "/gxboxlive.php");
If you throw together some inline code to output the result of that to the Admin console then you see a bunch of Access Denied messages.
Now, it is possible to remove all the query parameters in that string above and it starts to work again.
However, I strongly suspect (with no actual evidence) that Microsoft has banned all requests with that query string involved and their Community Developer terms of service explicitly state that they reserve the right to ban any site or application they consider to be abusing their system.
As a result, I
strongly suggest that, if you fancy your hand at hacking out the query string, that you also ensure the gXboxLive scheduled task runs no more than once per day. Abuse may lead to banning and I didn't see any right of appeal.
YMMV but good luck.