This piece of code is not working

[zmmmzz]

Im trying to display a users' avatar in navbar. I add this lines to a plugin in the global_start hook location.

PHP Code:

// include backend
require_once('./global.php');
require_once(DIR . '/includes/functions_user.php');

// setup avatar if exists
$avatar = fetch_avatar_url($vbulletin->userinfo['userid']);
if ($avatar != '' AND $vbulletin->options['avatarenabled'])
{
    $avatarurl = $avatar[0];
} 


Then the html in the navbar template:

<img src="$avatarurl" alt="Your Avatar" border="0" />

The avatar won't display. What am I doing wrong?