SAP Message TU175 - Main portion &1 is not an MDE portion; allocation is not permitted

Diagnosis
PDC meter reading unit &V2& may only be assigned another PDC meterreading unit as its leading meter reading unit. You cannot assign PDCmeter reading unit &V2& to leading meter reading unit &V1& because &V1&is not a PDC meter reading unit.

Procedure
Delete the number in field "PDC number" or assign a PDC meter readingunit as the leading meter reading unit.