I have an ipod nano 4th gen, and i manually add the album art. MOST of the time it works fine, but on a few songs/artists i added recently it just wont work. i put album art on, and then on my ipod it just shows up as a black square. this happened for 9 albums. i tried a lot of different album covers, from around 150x150 to 350x350, but nothing works! does anyone else have this problem? and how can i fix it?