SAP Message TU174 - Main portion &1 is MDE portion; allocation not permitted

Diagnosis
Meter reading unit &V2& will be assigned to leading meter reading unitV1, which is a pdc meter reading unit. this is not allowed.

Procedure
Set a number in field "PDC number" (which changes meter reading unitV2 to a pdc meter reading unit) or assign a meter reading unit thatis not a PDC meter reading unit as the leading meter reading unit.