ME706 error for logistic invoice verification

Hello.

In a inter-company scenario we would like to obtain a logistic(MM, MIRO-like) invoice generated with the use of EDI message(INVL process code).

Question nr. 1: What could cause the fact that EDI message remains in 51 status and the error message is:

"Item of purchasing document xxxxxxxxx does not exist" (Message no. ME706) where xxxxxxxx is the number of the initial (NB type) PO. In our process the first line of the PO is always deleted and add a second one is added after PGI done form the manufacturing plant - this is needed because we use different material codes between company codes.

Is there a way to overcome this problem?

Question nr. 2: We would like to have the RD04 message only after PGR is done, is there a standard way to achieve that?

Thank you in advance.