How can I get simple html dom working in my Wordpress Plugin?

I have a short php file that collects data from a certain URL using Simple HTML Dom.

This script works fine when I run it, but I'm trying to include it in a Wordpress plugin and save the values in some custom fields but it fails with the following error.

PHP Fatal error: Call to a member function find() on a non-object in /Users/duncan/Webserver/wordpress/wp-content/plugins/booking-scores/simple_html_dom.php on line 1113

The code I have is as follows:

<?php
include_once('../../../wp-load.php');

$site = get_field('booking_url', 'options');

include_once('simple_html_dom.php');

$html = new simple_html_dom();

$html->load_file($site);


// get values...
$score = $html->find( '#review_list_main_score', 0      )->innertext;

etc...

this is fine running on its own, but once it is in the plugin with

include_once('../../../wp-load.php');

$html is always a non-object.

Is Simple HTML Dom not compatible with wordpress, or is there something I am missing here?

via Chebli Mohamed