Install gnome-control-center from synaptic and then launch gnome-control-center from a terminal (or create a shortcut to /usr/bin/gnome-control-center). Browse to Network->Network Proxy now set the proxy as required and click on the apply system wide button. This should resolve your problem.
Ok guys, I have found a work around...
Install gnome-control- center from synaptic and then launch gnome-control- center from a terminal (or create a shortcut to /usr/bin/ gnome-control- center) . Browse to Network->Network Proxy now set the proxy as required and click on the apply system wide button. This should resolve your problem.