Deficit of PU IR quantity

Dear all,

I'm on SRM 7.0 SP09, classic scenario, and we're using the evaluated receipt settlement (ERS) process (in SAP ERP backend). When I want to create a return delivery in SRM, I get the error message "Deficit of PU IR quantity 3,000 PC".

I know that it is (normally) not possible to reverse a confirmation when the invoice is posted. But is there a way to do it with ERS and credit memos? I thought that I can create a return delivery and then as a follow-on document to that a reverse ERS document is created.

Any help is appreciated!

Regards,

Karsten