How do I require_once()?

I’m trying to require_once a file in another directory in a WP plugin. I always get “This plugin has been deactivated because your changes resulted in a fatal error.” when I activate the plugin. When I remove require_once() everything works fine (well not ‘fine’) but there are no errors. This is just the piece of the code that I’m having trouble with. 🙂

Is there another way to include an external file in a WP plugin? (as for the file to be included, it’s at “/home/DIR/public_html/SITE/FOLDER/global.php”)

<?php
$vwd = ‘/home/DIR/public_html/SITE/FOLDER’;
$cwd = getcwd();
chdir($vwd);
//only the next line causes a fatal error.
require_once(‘./global.php’);
chdir($cwd);
?>