What are you using for a bootloader? Grub2? isolinux? Whichever, you forgot to post the menu entry which you are using to try to boot it. We can't tell you what is wrong if we don't know what you've done.
The following entry is one I use to boot SystemRescueCD from a DVD with Grub2:
Code:
menuentry "SystemRescueCD" {
linux /isolinux/rescuecd
initrd /isolinux/initram.igz
}
For that to work, you would have to loop mount the SystemRescueCD to another folder, then copy its files to the root of the filesystem. If you have it on a flash drive, you will probably need a drive/partition entry on the loopback loop line as is shown in the Linux Mint entry in the link you posted.
Post your grub.cfg or isolinux.cfg file or whatever you are using.