[ubuntu] Automatic updates could not be installed.

view full story

http://ubuntuforums.org – Today I got "automatic update" notice from ubuntu 10.04 but while trying to install it, it failed with the message that requested website (something like http://security.ubuntu....) could not be found. I have never faced such issue. Why is this so and what should I do? There were updates for latest firefox etc. (Hardware)