Display posts with \'Product\' type ordered by \'Price\' custom field:
$query = new WP_Query( array ( \'post_type\' => \'product\',
I think this changed slightly in Wordpress 3.7.
I had to change
return str_replace('menu_order', 'mt2.meta_value, mt1.meta_value', $orderby);
into
return str_replace('wp_posts.menu_order', 'mt2.meta_value, mt1.meta_value', $orderby);
Thanks for the initial solution! [Edited]