You can't use a used RW disk even if it has been erased, you need a clean new disk and probably might be better to have one that is not RW, if RW is not a prerequisiste for a System Repair disk. Burning to a RW disk will require you to DISABLE mutli-session.
Sometimes it's better to disable Burn verification, that option is usually only for data disks that do not have executables or volumes of folders, best for mp3 disks or avi files etc..