Diagnosis
Either you have not yet created any handling units nor any scrapquantities or the handling units you created cannot be backflushed dueto the error status.

Procedure
If you have not yet created any handling units or any scrap quantities,then do so now and then carry out the function again.
If you have already created handling units but they still cannot bebackflushed, then you should check the error status of the handlingunit.