[CentOS] New kernel causes kernel panic/unable to mount root

Hi,

I've just moved over to an Opteron 246 dedicated server and have used
up2date to install the latest kernel (2.4.21-27.0.4.Elsmp).  However, when
the machine reboots it never comes back up and according to the datacentre
technicians, this is what's happening:

VFS: Cannot open root device"806" or 08:06
Please append a correct "root=" boot option
Kernel Panic:VFS:Unable to mount root fs on 08:06

The technician then needs to reboot with the original kernel
(2.4.21-27.0.2.Elsmp) to get it to work.  Apparently there are no third
party modules/drivers loaded.  This didn't occur when I did exactly the same
thing with a dual Xeon 3.06Ghz machine.  Both machines use SATA drives.

Any ideas?  Any pointers are greatly appreciated.  Incidently, lilo.conf
currently looks like this:

prompt
timeout=50
default=linux
boot=/dev/sda
map=/boot/map
install=/boot/boot.b
message=/boot/message
linear

image=/boot/vmlinuz-2.4.21-27.0.4.ELsmp
        label=newlinux
        initrd=/boot/initrd-2.4.21-27.0.4.ELsmp.img
        read-only
        root=/dev/sda6
image=/boot/vmlinuz-2.4.21-27.0.4.EL
        label=2.4.21-27.0.4.E
        initrd=/boot/initrd-2.4.21-27.0.4.EL.img
        read-only
        root=/dev/sda6
image=/boot/vmlinuz-2.4.21-27.0.2.ELsmp
        label=linux
        initrd=/boot/initrd-2.4.21-27.0.2.ELsmp.img
        read-only
        root=/dev/sda6

Regards,

	Martyn