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When I run update manager, Ii get following error.
I am using Ubuntu 12.04 LTS, 64 bit. I am new to Ubuntu please help me out.
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The reason is that this repository does not have packages for your version of Ubuntu (precise). Take a look at http://ppa.launchpad.net/crebs/ppa/ubuntu/dists/.
You need to remove this repository from your /etc/apt/sources.list file.
Find the lines that contain "crebs". They should look like
(or something like this). and put a
Repository is now disabled. Save the file, exit the editor and in a terminal, run
(there is also a GUI way of doing that via software sources or something similar from Ubuntu dash, but I don't remember where it sits)