syncing trouble; (won't write all music)

the ipod:
80 gig

the laptop:
mac: ibook g4

the issue:
*it syncs some of the music (mostly from the playlists) but not all of the general library. i have it set to sync all songs and playlists.
*itunes says: "Attempting to copy to the disk "michael's ipod" failed. the disk could not be read from or written to."

possible source of the problem:
i downloaded some music months ago in a crappy format (sorry can't explain it any better than that) and it gummed up the hard drive a bit (my mistake!). the laptop hard drive has been cleaned up and works fine. the ipod seems to need to be cleaned up as well.

i thought wiping the ipod clean and reloading everything from laptop would be a good way to go. i restored it and got the same error, and now it has even less music.

what do you think?

thanks!
-michael