I had the same problem (parted unable to resize ext3 partition with knoppix on it...see post http://www.knoppix.net/forum/viewtopic.php?t=13566) I ended up using fdisk (linux fdisk, not MS fdisk) which meant the knoppix install was trashed.
Why do you need to resize? Are you running out of space? You can maybe get around resizing by creating a new partition then moving /home or something to it so your knoppix install is spread over two partitions. Or you could remove some unneeded applications to free up some space.