SAP Message AO044 - Order &1 has the wrong order category &2 - please correct

Diagnosis
You want to assign order &V1& to the appropriation request.
According to its order category &V2&, the order is neither an internalorder nor a maintenance order.

System Response
It is not possible to assign the order.

Procedure
Correct your entry.
You can only assign orders with the order category for internal ordersor maintenance orders.