An earlier Google reference to On-Disk.com cached on Google reads as follows:

Knoppix 6.4.3 Live DVD
Jan 13, 2011 ... Like previous versions, Knoppix 6.4.3 incorperates newer ...
the integrated ATI radeon graphics adapter does not work with the accelerated ...
on-disk.com/product_info.php/products_id/1301 - Cached

This On-Disk site was updated Jan 23.

Perhaps some 6.4.3 DVD isos are (or were ) corrupted.