Did you do a md5sum of downloaded Knoppix Iso.
It would help also if you showed what version of Knoppix 6.2 Iso you downloaded (32 bit or 64 bit copy and paste version) and from where you downloaded ISO from (link).
What burning program also are you using? Are you trying to do this with in Windows or Linux (what version of Operating System)? Edit: looks like you run Windows 7)