» Fri May 27, 2011 9:40 pm
Writable CD's can be written single-session (usually used only for major file backups that you don't want overwritten) or multi-session, which lets you add more files later. It would appear that the disk you're trying to add files to was recorded single-session, so you'll need a fresh disk to write to.
If your system has one read-only drive and one read/write drive, you might have the disk in the wrong drive. You'd normally have the game disk in the read-only drive and a writable CD in the other, but the game will run if its disk is in the wrong drive, so you'd only find out when you try to write to the other one!