You should never convert from one lossy format to another, like mp3 to m4a.

I think I've guessed what your problem is: You're trying to drag & drop the songs from the LW playlist within iTunes. Please see the Sticky at the top of this section about how to get the songs into your iTunes music library. If they're not there iPod will not import them. The LW playlist is simply a playlist & the actual songs still sit within your LW downld folder!!!