Error : Document contains same order item more than once in IDOC

Question

We have Intercompany IDOCs getting created in our system. The
trigger for this is the Billing Document in the same system in
differenct company code. The MEssage type being used is INVOIC and the
basic type is INVOIC01.
The IDOC is in the status of 51 with the error message
Document contains same order item more than once
Message No : M8 321.
Can anyone tell me why raise this error and how to resolve it?
Thanks.

Answer 1

What I have recently learned is that in 6.0 SAP allows the same line item to be on an idoc multiple times.  However, the item has to be GR-based-IV and there has to be a unique entry in the delivery note of the GR.   I have successfully tested this in my development system.  
What I can't get to work is if the GRs have the same delivery note value.   What I think is happening is these GRs are not unique so SAP cannot match a GR with an IR so it fails with this error. 
Here are the examples:
Works 
GR# A           deliverynote/BOL    "abcd"
GR# B           deliverynote/BOL     "efgh"
Invoice idoc
e1edp02    qualifier 016          abcd
e1edp02    qualifier 016          efgh
Doesn't work:
GR# A           deliverynote/BOL    "abcd"
GR# B           deliverynote/BOL     "abcd"
Invoice idoc
e1edp02    qualifier 016          abcd
e1edp02    qualifier 016          abcd
If anyone knows of a way to make the second scenario work, I'd like to hear your solution.
Thanks
Sandra