When you open up a song in cubase it looks for the files that are associated with the tracks recorded in that song. If you have moved the files to another folder or if you sent them to the wrong audio folder to start with, it will give you a choice of letting the program look or you manually look where the files are. If you let the tracks be named by default when you record (e.g. track1, track2) there is little chance you will find the correct file to go with the track. If you have deleted the file you will also get a not found message. At any rate the problem you are having is because Cubase does not allow you to freely move tracks around in windows like most programs do. Dang, I hate when that happens.
