Closing a Production Order
For closing a Production Order
1) check in session ticst0101m000 wether some quantities are pending (esp. against subsequent delivery)
2) If production order is attached with a P.O. (Subcon) then ensure that first the PO is processed till PDPO stage.
You can also check the planned inventory transactions by item session and see wether something is pending against the production order.
Hope the above helps.