I now it's an old post but i had the same problem and this was the only
thread that kept coming up with a search so i put my findings here.

Please note that i use no giftsertificates etc just a plain offline order,
so i don't know if stuff like that needs the payment_wait.php.

Find payment/payment_offline.php


in there find

include $xcart_dir."/include/payment_wait.php";

Just delete it and your done

cheers Eddie