I never tested to remaster Knoppix DVD with kn-remaster
Now I did it and found, it doesn't work without enough RAM; the new '/opt/knx/KNOPPIX/KNOPPIX' will not be created. Therefore the ISO gets the wrong size.

Next time I'll test it on a not virtual machine with 4GB RAM in a separate partition.

Also with "kn-recombine" and Knoppix DVD flash disk installation you need a lot of RAM and a not virtual machine.