Can you reproduce the problem? What happens if you add a new order? We need to figure out why it is failing in order to come up with a strategy to fix it. There has to be something different about the orders that do and don't succeed.
Did they used to show and now don't? Have you maybe deleted the products that were sold from the store or updated the database in some way? Did you get the confirmation emails? We'll need more information in order to debug the cause of this problem.