Install groovy o 12.04,Hash Sum mismatch?

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I follow the instruction : Ubuntu 12.04 (Precise)

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu precise main" > /etc/apt/sources.list.d/ros-latest.list'

Set up your keys

   wget http://packages.ros.org/ros.key -O - | sudo apt-key add -

sudo apt-get update

then ,that is this :

Hit http://packages.ros.org precise Release Get:1 http://packages.ros.org precise/main i386 Packages [1,641 kB] Ign http://packages.ros.org precise/main TranslationIndex
Hit http://packages.ros.org precise/main Translation-en Ign http://packages.ros.org precise/main Translation-en_US Fetched 1 B in 3s (0 B/s) W: Failed to fetch gzip:/var/lib/apt/lists/partial/packages.ros.org_ros_ubuntu_dists_precise_main_binary-i386_Packages Hash Sum mismatch

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

then ,I type:

sudo apt-get install ros-groovy-desktop-fullat
that is this:
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros-groovy-desktop-full

I then check the directory:

bob@bob-robot:/etc/apt/sources.list.d$ ls ros-latest.list

I have search the similar answer,it may be the source problem , so how to solve it? many thanks ,I am waiting the answer...