I managed to remove enough software to bring the size...
If you remove packages within Knoppix, it's on your own risk. Did you get any error messages from aptitude? Did you test your burned ISO with cheatcode "knoppix testcd"?

For CD remaster with kn-remaster script I suggested
http://www.wp-schulz.de/knoppix/kn-c...html#vorschlag

Perhaps it may help you.