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I get the following error when trying to update Ubuntu:

W:Failed to fetch  Unable to connect to
, E:Some index files failed to download. They have been ignored, or old ones used instead.
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Choosing a different server often fixes this problem - good luck – Malee Oct 29 '12 at 12:39
when i chose the bestServer i got "No suitable download server was found" and Please check your Internet connection. – كنعان المشني Oct 30 '12 at 10:48
Contact your netwrok admin and make sure that your port no 8080 is not blocked. – K.K Patel Nov 8 '12 at 6:00

You should give some more detail, like are you working behind proxy. Some time working behind proxy may cause this kind of problem. If this is the case then you can edit your apt.conf file. Use this command:

gedit /etc/apt/apt.conf

Then add the following line at the end

Acquire::http::proxy "http://userid:pass_word@proxy:port/";

Where useid and pass_word are you proxy authentication user id and pass word.
You can check this link for reference

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I think its a problem with the latest Ubuntu update. I get the same problem here.

" precise Release: The following signatures were invalid: xxxxx Ubuntu Archive Automatic Signing Key

Changing it to main server doesn't help either. It looks like these guys have broken the code. Many people searching on the topic and the freshness of the discussions says something ain't right.

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Welcome to Ask Ubuntu! Please do not post such "Me too!" comments as answers, but (once you have gained enough reputation to do so) as actual comments or upvote the question. – user98085 Nov 23 '12 at 13:39

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