If the file were corrupt I don't think iTunes would play it then either. Maybe there was a glitch with the transfer, try to resync it. If that doesn't work then you may need to find another copy of it. Search the iTunes store for it, those are all high quality mp4s.

The difference is that the mp4 is more hardware intensive but had twice the compression quality. A 128K mp4 is approx equivalent to a 256K mp3.