Why can my uploaded cd music not be found in its original location?

Hi,

I just bought an ipodnano 7th gen and when I connected it, it only downloads purchased music. I tried to play my downloaded cd music in itunes and it says unable to locate file in its original location. All of my music is still on an older ipod with video but when I sync up it does not transfer the music back to the computer. If anyone can help, it would be very much appreciated.