Index: units/orders/orders_event_handler.php
===================================================================
--- units/orders/orders_event_handler.php	(revision 13919)
+++ units/orders/orders_event_handler.php	(working copy)
@@ -1247,7 +1247,9 @@
 	 */
 	function CheckUser(&$event)
 	{
-		if ($this->Application->isAdminUser) {
+		if ($this->Application->isAdminUser || defined('GW_NOTIFY')) {
+			// don't check for user in order while processing payment
+			// gateways, because they can do cross-domain ssl redirects
 			return;
 		}