Items waiting to be shipped?

[ApplianceJunk]

At the bottom of our store there is a admin box.
At the bottom of the box it says, "Items waiting to be shipped:1"

I have been able to mark all the current items as shipped, but this one seem to be to old to mark anymore.

When I click on the "1" I get taken to the "Transactions" page were I can see that one order.

After clicking on "Order Detail" I would normally mark it shipped, but on this one item when I click on "Order Detail" I get this message.

This is an older transaction. Order detail does not exist. Please use export transactions to gather information on older transactions

How can I clear this one item so it no longer shows me that one item is waiting to be shipped?

Thanks,