Manual reservation for order category & not allowed

What causes this issue?

You entered an order whose category only permits automatic
reservations. The following order categories do not allow manual
reservations:
10,,PP production order
20,,network
30,,maintenance order
40,,batch order (process manufacturing)
50,,inspection lot

System Response

The system does not accept your specification.

How to fix this error?

Enter a different account assignment, or cancel the
processing.
If required, check whether any reservations for the specified account
assignment already exist.
<DS:TRAN.MB25>Proceed</>

Error message extract from SAP system. Copyright SAP SE.