Thrid Party PR and PO

Scenario:

#1 Sales order is created with item category equivalent to third party (This creates a PR internally)

#2 Referencing this PR, PO line item is created (No goods receipt is done with respect to this PO)

#3 PO line item is deleted for business reason

#4 Somehow (user has now deleted the PR line item corresponding to this PO line item - This generally does not happen as account assigned PR can only deleted through sales order)

#5 Now, if i try to delete Sales order line item, getting a message 'Line item can not be deleted because of subsequent document (referencing PO number).

I have to delete this sales order line item; How should i proceed. Kindly help.

Regards

RJS