JJ2 doesn't like .it files. I would guess most problems with .it tracks outside of size have to do with the instruments used. There's a good chance the track wouldn't sound right in JJ2 anyway. If downsampling doesn't help, I would suggest either trying to convert it to some other format (which may have some undesired effects) or trying to find another song (preferably not .it). I don't think converting the file to a j2b will help in this situation.