You cannot reset to draft asset "%(asset)s" because it has lines. You cannot delete asset "%(asset)s" because it is not in "draft" state. You cannot close period "%(period)s" because some assets "%(assets)s" still have lines without move. Invoice line can be used only once on asset. To invoice purchase "%(purchase)s", you must set an account asset on product "%(product)s". Asset can be used only once on invoice line. There is no started asset.