It took less than a minute to create the ISO image file.
Code:
Fr 17. Mai 09:25:15 CEST 2013
root@Microknoppix:/media/sda1/knx402# mkisofs -l -r -J -V "KNOPPIX" -o knx402.iso -no-emul-boot -boot-load-size 4 -boot-info-table -b boot/isolinux/isolinux.bin -c boot/isolinux/boot.cat master
I: -input-charset not specified, using utf-8 (detected in locale settings)
Size of boot image is 4 sectors -> No emulation
  1.41% done, estimate finish Fri May 17 09:25:17 2013
[...]
 99.85% done, estimate finish Fri May 17 09:25:42 2013
Total translation table size: 2048
Total rockridge attributes bytes: 5225
Total directory bytes: 12288
Path table size(bytes): 86
Max brk space used 22000
355562 extents written (694 MB)
You can find a link for downloading Knoppix 4.0.2 at http://www.distromania.com/distro_info.php?distro=332

I think possible reasons for I/O errors are a dirty or damaged DVD-ROM medium and a dirty DVD-ROM drive.
You could try to clean the DVD with water and some dishwashing detergent.
If there are serious scratches you could try some polishing paste that is intended for the repair of CD or DVD surfaces.