crash when using bare wordpress not from root

I’m trying to implement IPN support for custom payment processing, and WP is crashing when I simply try to load WP core from file that is not in root…

ipn.php:
define(‘WP_USE_THEMES’, false);
require_once(‘../../../wp-load.php’);

crash:
Fatal error: Class ‘DOPBSPUpdateAPI’ not found in …/public_html/wp-content/plugins/dopbsp/includes/class-update.php on line 79