Can't Boot Knoppix 4.0.2

I got Knoppix linux off computer buyer cd and burnt it as an iso on to a cd. It boots from the cd and it tells me to hit return to boot into knoppix. I do this and it says searching for usb and firewaire devices. This works but then it find te files it needs but then it says that it cannot find the main filesystem.
What is wrong with this?
How can i fix it?
Calum

Did you check the md5 to confirm that your download isn't corrupted?
If you find that your download is ok, I suggest burning it again, and use the slowest burning speed available.