Voice Memos On Ipod


I had several months worth of voice memos on my iPod. When I connected to my G5 today, half of them were removed. They show up in my Library but you cannot play them through the computer nor can you move them. When you try to drag them to the memos folder, itunes indicates that it cannot find the source. What happened? Why were they removed from my iPod? Can the memos be recovered? The information lost cannot be replaced? Please help, if you can. Thank You.