Disastrous failure (6)
(Other definitions for cropper that I've seen before include "Disastrous mistake or fall" , "Heavy fall" , "Come a --, suffer disaster" , "failure" .)
(Other definitions for fiasco that I've seen before include "Total debacle" , "Embarrassing failure" , "Abject failure" , "Ignominious failure" , "An utter mess or cock-up" .)