Why cant I open files on my back-up CD. I have a Windows Vista and I made a back-up

[Sunny]

of all the music I have in Windows Media Player. The back up completed. I put the CD in my computer, tried to "open" the files, I also tried using "explore" and once I try to "play" them the Windows Media Player opens but I get this message: Windows Media Player cannot open the file, might not support the file type or the Codec used to compress the file....They exist on my computer and I am able to listen to them, but WHY can't I open the files after I copy them to a CD? The whole purpose for a back-up is to be able to have them put aside in case something gets deleted or lost on the computer. I am frustrated because then I wind up throwing the "back-ups" away.

[mick f]

what ever compression tool u used is the one u have to open them with --- since that is how u stored them i wasn't there ---so this is a quess