MD660A Memory problem

was working just fine... i've been able to put files on it in the past just by dragging it into the folder. all of a sudden, today, i deleted songs to make room for new songs but after i delete a song, i can't put a new one one it, claiming that the memory is full. When I check properties, the memory *is* full but the #MB that the folder shows in the lower right corner says an amount that is WAY less than full. I have no idea how to fix this, please help! was working just fine... i've been able to put files on it in the past just by dragging it into the folder. all of a sudden, today, i deleted songs to make room for new songs but after i delete a song, i can't put a new one one it, claiming that the memory is full. When I check properties, the memory *is* full but the #MB that the folder shows in the lower right corner says an amount that is WAY less than full. I have no idea how to fix this, please help!