Deleting an intercompany PO

I would like to delete an open intercompany purchase order but receive an infolog saying “Order line must be invoiced first.”

The item referenced in the info log has never been received. If I try to delete the item I am told that it will change the sign. Then if I try to 0 the quantity ordered I am told that the sales order is being updated and my update has been cancelled.

So, how can I delete this purchase order from my system?

Thanks for any help you might provide!