Ubuntu boot failure after Linux headers update.

This is a problem I've had before and I've even gone to re-installing the OS because it just wouldn't boot.
Seems the problem is that the /boot/grub/menu.lst is substituted with a new one containing ONLY Ubuntu (incl. recovery) and MemTest. However, the kernel line contains a reference to UUID (in root=UUIDxxxxxxx...xxxxxx) which seemingly is not recognised. So, the real root is not reachable.
However, as Ubuntu can't boot, can't get at /boot/grub/menu.lst to fix it.
Becuase Ubuntu can't boot (and this is where the MBR is) nothing else can boot.
So, a BIG problem.
However, using the Gutsy install CD, which allows access to the internal HDD and the non-bootable Ubuntu, I was able to take out the UUID in menu.lst and substitute /dev/sda3 and then it booted fin and everything worked again.
I posted on this here (post #122) as some other guy had a problem with initramfs showing up as a shell when his system wouldn't boot. This gives more detail on what I did.