i am the simple fyer...

The first thing I'd check is the checksum on the iso you burned.
The second thing I'd check is the CD after you burned it.
Mount it with the loop command and browse it to see if things look alright.
If you can't do that then cut your CD burner speed in half and burn a new CD.
ok, sometimes when you download things, it doesnt download correctly... some bytes instead of being a 1, are a 0... and i think i saw a 2 (joke joke, bender). any way... there are some programs that will check this...

also, same thing happens when you burn to CD... well, the jists of it... but i wont complicate it as much... so, turn down the burning speed... i usually burn at 8X... slow as... but hay... it stops all the problems... so you need to burn a new CD... and then try it all again...

also... make sure that the "sudo knoppix-installer" code is all in one line...

hopefully i simplified what GreyGeek said (dont hit me)...