update-grub problem

["John Fleming" <john@wa9als.com>]

I'm trying to install linux-image-2.6.18-6-686 using apt-get.  I recently 
made the recommended change in /etc/kernel-img.conf to include:

postinst_hook = usr/sbin/update-grub
postrm_hook = usr/sbin/update-grub

When I run the apt-get install...., the configuration fails with the error 
about
"Could not find postinst hook script [usr/sbin/update-grub]."

However, that script DOES exist in the stated path.  So what gives with 
this?

Thanks any help!  - John