Document contains some order item more than once - invoice verification

Question

Hi,
we have one cross company stock transfer process in which when a billing is created in SD side, an IDOC will be triggered automatically and create an invoice verification at the MM side.
The problem is some of our billing of this process having an IDOC application error that said.
Document contains same order item more than once
Message no. M8321
Diagnosis
Under the following circumstances, you can settle an order item in an invoice received via EDI more than once:
- Goods-receipt-based Invoice Verification has been defined for the order item.
- The IDoc contains the delivery note numbers of the goods receipts.
System Response
If this is not the case, the system cancels posting of the IDoc.
Question:
1 - The funny thing is IDOC showing 51 IDOC error code message on status record of INVOIC. But the invoice verfication get created in PO history.
2 - I think this error is because we need to make the PO as GR-based Inverifcation. We have flagged it in Vendor master, and Info record, but this indicator is not flag automatically in the PO (and we cannot manually change the PO as this indicator is grey-out). How?
3 - how to solve this error?
Thanks

Answer 1

Once PO history is created, you cannot change the "GR-based-IV" flag. Two options are there before you.
1. Cancel all the GRs & Invoices posted in the STO then system will allow you to update the GR-based-IV flag. After updating this flag repost the GRs and invoices.
2. Create a new STO, now since you have updated the vendor maser & info-record, this flag will automatically get updated during the STO creation itself.
First option is tedious and should be selected only if you can go option 2 is not at all feasible