Dual boot problem - Vista disappeared from Grub menu

[Colin Law]

Hi

On a machine with dual boot Ubuntu 10.04 and Vista which has been
working fine for many months, suddenly Vista no longer appears in the
boot menu (GRUB2).  I have not used Vista for a week so am not sure
exactly when it happened.  I am not aware of any problems in the
meantime apart from an update (don't know what to) which complained of
a download not being available, but this seemed ok when the update was
run again later.

I have checked /etc/default/grub and run
sudo update-grub
which does not report the Vista partition.
I am able to access the files on the vista partition from Ubuntu and
it looks ok in gparted (showing the boot flag).

Google reports lots of issues with grub disappearing after updating
windows but I could not find any reports of Vista disappearing.

Any suggestions will be much appreciated.

Colin