For a command

sudo apt-get update

I get following error

W: Failed to fetch http://ch.archive.ubuntu.com/ubuntu/dists/maverick-updates/multiverse/binary-i386/Packages.gz 407 Proxy Authentication Required ( The ISA Server requires authorization to fulfill the request. Access to the Web Proxy filter is denied. )

I am running Ubuntu 10.10 installed on Windows XP using VirtualBox. For internet connections I am using proxy server with an authentication. I tried to use gnome-network-proxy tool to set proxy settings system-wide.

After that /etc/environment has been updated by http_proxy variable with the format http://my_proxy:port/, there were no authentication data.

I checked this with firefox. Browser asked my for login and password and everything was working fine. It was unfortunately not the case for apt-get. I have also tried to do as described here. Unfortunately it does not work.

May it be somehow related to the fact that a proxy is in a Windows domain, any ideas ?

EDIT:
My proxy name is http-proxy. Is '-' a special character here ?