Problems using itunes files on Rekordbox

I'm a novice flx4-user and was excited to use my extensive library of tracks from iTunes in Rekordbox. Turns out that mostly isn't possible (I realize I could've googled my way to that conclusion prior to.) However, I managed to convert the files from one playlist using TuneCable (something I've since realized is not kosher but here I am) That was great, except about half of them won't play in Rekordbox and, in fact, makes the program crash (spinning mac ball) when I try to load them. All the files are M4A and I don't see a difference between them. But some of them work just fine and some of them don't.

If anyone has any leads on how to resolve this, I'll be most grateful. I've ended up spending all my time trying to fix these technical issues rather than practicing and playing with my new equipment. Thank you in advance!