Without any more data on the scanner, it would be hard for me to make suggestions even if I had known a lot about scanners and xsane, and I don't!
Part of the reason I don't know anything, is that I have had no problems with xsane scanners in recent Knoppix releases, they just work. One might suspect some program error here.
But, as Ubuntu 11.04 should be very close to 6.7.0, I suggest you collect as much information from the working configuration as you can, and then try to figure out what goes wrong in Knoppix. Eventually try to manually configure it the same way as it is in Ubuntu. You might even try installing Ubuntu's drivers etc. Taking a backup copy of your persistent store before you try will let you rollback if something gets broken.
Good luck!