SAP Message V1846 - You cannot change field &1 due to the system configuration

Diagnosis
The value in field &V1& is set by the configuration.
You cannot change the value in this field. This is due to one of thefollowing reasons:
You cannot change the configuration for this item.
The status of the sales order does not allow you to change theconfiguration.
The value consists of object dependencies and therefore cannot bechanged.