subcontracting and PM orders

Hello,

I have activated business function LOG_EAM_ROTSUB for subcontracting.

When trying to go through process where returned material is different then the one sent to subcontractor

Iu2019m getting following error message when trying to convert PR into P.O. : Material number 10000766 does not equal material number 10000170 of order item

Message no. AD_SUBCON013

In the maintenance order I have two materials assigned into subcontracting operation:

Material 10000170 with MPI Rework material to subcontractor

Material 10000766 with MPI Rework material from subcontractor (with negative value)

Do you have any suggestion what causes above mentioned error message?

Many thanks for your clues

Grzegorz