A Knoppix 3.2 DVD??? Where did you get such a thing?

The error you have usually indicates either an incorrect procedure used to burn the disc (including not checking the md5 sum, not burning the iso file "as an image" and/or burning at a high speed rather than a slow speed like 4x) or hardware problems reading the disc. If it's hardware problems reading the disc (I have my doubts) then you might resolve it with the "cheat code" "knoppix nodma" at the boot prompt, but if I remember version 3.2 properly, nodma was the default back then. So I'm guessing that you should follow the documentation link at the top of this page and read the downloading faq to see if that doesn't help clear up the issue.