For some reason insserv is no longer on the path in 12.04. Anyway in Glenn's instructions replace the line:
sudo /usr/lib/insserv/insserv calibre
If you google it various places will tell you to make a sym link so that it's on your path e.g. here
but that's up to you.
Attached is an updated "calibre" file based on the 12.04 /etc/init.d/skeleton.
Disclaimer: I tested this on Linux Mint 14 rather than Ubuntu 12.04 itself though I don't believe there are any differences in this regard.