Marketpress 3.0 updating the order status gives Fatal Error

I have upgraded my multisite installation of Marketpress to the new beta version Prices and skus remained in this update - Hooray.
But when I try to update the status of an order, I get the following error
Fatal error: Call to a member function get_items_as_objects() on a non-object in /nas/wp/www/staging/webonmission/wp-content/plugins/marketpress/includes/common/helpers.php on line 86