Downloaded bfbc2 on my hardrive but still says unreadable?

i donwloaded another copy of battlefield bad company2 to my hardrive b cause my xbox fell and scratched the disc and i heard downloading it to myhardrive will letmeplay itand i did download it but everytime i start toplay it it still says discunreadable even though it checked to see if i had the game what do i do?Downloaded bfbc2 on my hardrive but still says unreadable?
Downloading it to your hard drive does nothing to still need the disc to play it.