Background
The user sees a "Nothing to Ship" warning for all orders with line items.
Cause
All items on the order are marked as "Needed". They are backordered because the item is out of stock (there is no quantity on hand).
On the View Orders dialog box, look at the Ordered, Shipped and Needed columns where the line items are displayed. You will see something like Ordered=1, Shipped=0, and Needed=1. This signals that the item is on backorder and removes its price from the sale total until you replenish your inventory.
Solution
If you do not drop-ship, turn off inventory tracking by setting the CheckInventory parameter (Order group) to False. This tells the program to assume all items are in stock.