On CD's, you cannot change files, replace them etc.... You can burn them to the CD, from there they are only Read Only files which means that you can Only Read them from the CD, Not change them.

It isn't really anything you did or didn't do. You get that message due to only being able to Read from a CDR.

CD's aren't quite as good when it comes to that as a Floppy disk. You need to make sure you have the files the way you want them before you burn them to disk. Thats why if you have files that you Update frequently, it is better to keep them on Floppy or Zip disk.

Hope this makes sense.