I see the following messages from both primary and alternate Ubuntu and Kubuntu Live Cds.
error: "prefix" is not set.
then,
booting a command list
you need to load a kernel first
Both these messages are displayed very early in the boot process, the first just after the boot begins and the second immediately after I select from the "Try or install" menu.
Selecting any option from "Try or install" leaves the system locked that needs a hard reboot.
I always see this on Live Cd's of Ubuntu/Kubuntu 12.04. But never on a Live USB.
Best Answer
You say 'burnt onto a CD'. It should be on a DVD as it is oversized. Brasero would tell you that. If you used a buggy CD burner it might have burned you a buggy CD. This is why you are not getting the problem with a USB stick.