An increasing number of music files in my iTunes are showing an '!' alongside them. These are files I have downloaded from original disks, and now if I try to play them, there is a dialogue box that pops up telling me 'The song 'xyz' could not be used because the original file could not be found. Would you like to locate it?' WHY is iTunes doing this to me? Do I have to start reloading all the music off the original disks again?