My customer placed an order, payment was confirmed and order confirmation email was received, however the order is missing in My Acocunt.  When I go to the backend, I can see that missing order is still in his shopping cart.  The order has not shipped and invoiced and the order is still missing and stuck in the shopping cart.  He placed an order 2 days prior to this order and it went through just fine.  What would cause this and how do I fix it?  Thanks.