PHP Hook not working

[mcyates]

I have a hook on vb 3.5 which is the following:

product: vbulletin

hook location: ajax_start

Title: adverts

Plugin PHP code:

<?php
ini_set ("include_path", ini_get ("include_path") . ':../:../../:../../../:../../../../');
include ('myfootball-ads.php');
echo $ad_network;
?>

Plugin Active: Yes

and this works fine when i put the $ad_network code in the footer, but its not showing up when i put it on the new version of vb version 3.6 BETA 4.

Why is this?

Thanks in advance.