custom k12 3rd cd

[Paul Pianta <pantz lqt ca>]

i have been trying to modify the 3rd cd of the k-12 - 3.1.1 set and add 
a couple of post installation custom rpms.

Basically i have included a new directory on the cd that i copy across 
to the hard disk during the post-install phase of my kickstart config. 
After that i install some rpms from this directory and copy some files 
to different places. (got the idea from the university of buffalo custom 
rh distro)

My problem is when i am asked for the 3rd cd - my custom cd is not 
recognised as being valid. I even checked how the k12 3rd cd was created -
mkisofs -A 'K12LTSP 3.1.1' -V 'K12LTSP 3.1.1' -r -J -T -o ../3.iso .

and used the same command to create my custom cd.

am i missing some validation step?
does anyone have any ideas?
should i be posting to the k12 list?