What's the cause / reason of: "unable to resolve host WS24 !?

[SYNass IT Ubuntu / Linux]

Hi Linux / Ubuntu experts and cracks
My wife's notebook has Hardy 8.04-RC / LTS installed.

At systemboot menu.lst shows 2 sets of bootables and 
I wanted to mark one of the sets with # to avoid displaying.

This happens:

xyz at WS24:~$ sudo gedit /boot/grub/menu.lst
sudo: unable to resolve host WS123
xyz at WS24:~$

What am I missing or doing wrong ??

TIA for your help, hints and suggestions.
Cheers, svobi