persistent home in /dev/hda6(KNOPPIX)

Why can´t i set a persistent home
on the same harddisk partition
where i have the folder /dev/hda6/KNOPPIX
created with the cheat code:
knoppix tohd=/dev/hda6

i get the error:

the knoppix configuration could not be saved
mount: /dev/hda6 already mounted or
/media/hda6 busy

mount: according to mtab, /dev/hda6
is mouted on /cdrom

what to do?
regards
flaviusaetius