vBulletin newbie coder.

Hi there. My website uses vBulletin with a vBadvanced-powered main site. It's been running fine for a year and I'd now like to expand the functionality of the main-site.

We've been using Farcaster's Event Attendance (which allows users to sign up for calendar events via a form on the calendar event template.

What I'm trying to do, is move this event-signup functionality to the main site. So firstly, I'm trying to write a script for vBadvanced that fetches a list of every signup for a given event.

The custom table is along the lines of this:
eventattendance(userid, eventid, ...)

And the code I have written is as follows:

<?php

/* get eventid passed from URL */
$eventnumber = intval($_GET['eventid']);

$query_eventattendance = $db->query_read("
SELECT user.username, user.userid, eventattendance.userid, eventattendance.eventid
FROM `user`, `eventattendance`
WHERE eventattendance.eventid = $eventnumber AND eventattendance.userid = user.userid 
ORDER BY user.username ASC");


while ($eventattendance = $db->fetch_array($query_eventattendance))
  {
   $newparticipant['eventattendance'] = '<li>' . $eventattendance['username'] . '</li>';

eval('$home["$mods[modid]"][\'content\'] .= "' . fetch_template('adv_portal_eventattendance') . '";');
}

?>

When I visit index.php?page=participants&event=*whatever*, I get a completely blank page outputted i.e. not a single character of HTML outputted.

Can anyone help me out?