some mp3's won't upload to a player.

I have a rather large mp3 collection, and they are all set up in itunes, perfectly fine. But i use an older itouch with ios 4.2 just for general music. im finding there are certain albums that wont upload to the player, even though they work within itunes. it just hang up and sits there trying to upload them during the sync. is there anything i can run to maybe re-encode them to be more compatible? Any thoughts?