I've noticed that if I use a persistent image file and for some reason it gets corrupted (powering off abnormally) that I'll get a bunch of filesystem errors in dmesg. I can fix it by booting with the "noimage" cheat code, like "knoppix64 2 noimage" and then run "fsck.ext2 /mnt-system/KNOPPIX/knoppix-data.img" and then "sudo reboot".

It'd be really nice if there were an automatic check of the ext2 image when knoppix boots. It would also let you know if errors have crept into your filesystem since knoppix still works but you see weird messages like "unable to write /etc/fstab".