problem in installing ros hydro

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I am using Ubuntu 12.04 after using 'sudo apt-get update' I get the following error Err http:// packages.ros.org precise/main i386 Packages 403 OK

W: Failed to fetch http:// packages.ros.org/ros/ubuntu/dists/precise/main/binary-i386/Packages 403 OK

E: Some index files failed to download. They have been ignored, or old ones used instead.

lastly i get

sudo apt-get install ros-hydro-desktop

Reading package lists... Done

Building dependency tree

Reading state information... Done E: Unable to locate package ros-hydro-desktop

my connection to Internet is through a proxy server. I have tried downloading from different servers but it is not working

please help