trouble with playlsits - playlists empty

hi, i’m new Sansa clip 2GB user and so far i’m more than happy. but today, a strange thing happened. i’ve draged and dropped some music to my player last night, and all my albums have playlists in it (i’m mostly using scene releases for try before you buy things). i’ve tried to play playlists right after i’ve finished with transfering music to my player, and everything was OK, all playlists were recognized by player. today, all lists are still there, but when i try to play them all i get is the message that the lists are empty. am i doing something wrong?