kernel-image "Kernel paic: VFS: unable to mount root fs"

[Jeff Penn <jeff@jrpenn.demon.co.uk>]

I was running Sarge on an Athlon cpu with ide/ext2 on a kernel compiled 
from kernel-source-2.4.18.  My system boots using grub from on a BSD 
slice.

After installing kernel-image-2.4.19-k7 & initrd-tools a reboot fails
with:

    VFS: Cannot open root device "hda5" or 03:05
    Please append a correct "root=" boot option
    Kernel panic: VFS: unable to mount root fs on 03:05

/boot/grub/menu.lst:
title   Debian
root    (hd0,4)
kernel  /vmlinuz root=/dev/hda5 hda=39813,16,63 idebus=66 devfs=mount
initrd=/initrd.img

The install of the kernel image created /initrd & the link /initrd.img.
I have also tried the above with & without devfs=mount/nomount, & read
through many similar problems on google.  The following have not made
any difference:

rdev /vmlinuz /dev/hda5
mkinitrd -o /boot/initrd.img-2.4.19-k7 /lib/modules/2.4.19/
(the above line is from memory - I used auto-completion when entering)

thanks
Jeff