I am newbie with Ubuntu.I am trying to download Okular pdf reader from Software Center but I am getting some error. At first it was asking for installation of packages from not authenticated source,when I click on Use this source it goes and do something like
upadating cache 
Then after some time it shows me this error:
I read this question "Requires installation of untrusted packages?"and tried to rebuild cache as given in first answer using :
sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update
and got this output:
yogeshwardancharan@ubuntu:~$ sudo apt-get clean
[sudo] password for yogeshwardancharan:
yogeshwardancharan@ubuntu:~$ cd /var/lib/apt
yogeshwardancharan@ubuntu:/var/lib/apt$ sudo mv lists lists.old
yogeshwardancharan@ubuntu:/var/lib/apt$ sudo mkdir -p lists/partial
yogeshwardancharan@ubuntu:/var/lib/apt$ sudo apt-get clean
yogeshwardancharan@ubuntu:/var/lib/apt$ sudo apt-get update
Get:1 http://dl.google.com stable Release.gpg [198 B]
Get:2 http://dl.google.com stable Release.gpg [198 B]
Get:3 http://dl.google.com stable Release [1,347 B]
Get:4 http://ppa.launchpad.net quantal Release.gpg [316 B]
Ign http://security.ubuntu.com quantal-security Release.gpg
Get:5 http://dl.google.com stable Release [1,347 B]
Ign http://us.archive.ubuntu.com quantal Release.gpg
Get:6 http://dl.google.com stable/main i386 Packages [1,227 B]
Get:7 http://ppa.launchpad.net quantal Release.gpg [316 B]
Ign http://security.ubuntu.com quantal-security Release
Ign http://us.archive.ubuntu.com quantal-updates Release.gpg
Get:8 http://ppa.launchpad.net quantal Release [11.9 kB]
Get:9 http://dl.google.com stable/main i386 Packages [710 B]
Ign http://us.archive.ubuntu.com quantal-backports Release.gpg
Get:10 http://ppa.launchpad.net quantal Release [11.9 kB]
Ign http://us.archive.ubuntu.com quantal-proposed Release.gpg
Get:11 http://ppa.launchpad.net quantal/main Sources [4,251 B]
Ign http://us.archive.ubuntu.com quantal Release
Get:12 http://ppa.launchpad.net quantal/main i386 Packages [14.3 kB]
Ign http://us.archive.ubuntu.com quantal-updates Release
Ign http://us.archive.ubuntu.com quantal-backports Release
Ign http://us.archive.ubuntu.com quantal-proposed Release
Get:13 http://ppa.launchpad.net quantal/main Sources [16.7 kB]
Get:14 http://ppa.launchpad.net quantal/main i386 Packages [39.4 kB]
Ign http://dl.google.com stable/main Translation-en_US
Ign http://dl.google.com stable/main Translation-en
Ign http://dl.google.com stable/main Translation-en_US
Ign http://dl.google.com stable/main Translation-en
Ign http://ppa.launchpad.net quantal/main Translation-en_US
Ign http://ppa.launchpad.net quantal/main Translation-en
Ign http://ppa.launchpad.net quantal/main Translation-en_US
Ign http://ppa.launchpad.net quantal/main Translation-en
Err http://security.ubuntu.com quantal-security/main Sources
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/restricted Sources
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/universe Sources
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/multiverse Sources
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/main i386 Packages
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/restricted i386 Packages
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/universe i386 Packages
404 Not Found [IP: 91.189.92.201 80]
Err http://security.ubuntu.com quantal-security/multiverse i386 Packages
404 Not Found [IP: 91.189.92.201 80]
Ign http://security.ubuntu.com quantal-security/main Translation-en_US
Ign http://security.ubuntu.com quantal-security/main Translation-en
Ign http://security.ubuntu.com quantal-security/multiverse Translation-en_US
Ign http://security.ubuntu.com quantal-security/multiverse Translation-en
Ign http://security.ubuntu.com quantal-security/restricted Translation-en_US
Ign http://security.ubuntu.com quantal-security/restricted Translation-en
Ign http://security.ubuntu.com quantal-security/universe Translation-en_US
Ign http://security.ubuntu.com quantal-security/universe Translation-en
Err http://us.archive.ubuntu.com quantal/main Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/restricted Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/universe Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/multiverse Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/main i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/restricted i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/universe i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal/multiverse i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Ign http://us.archive.ubuntu.com quantal/main Translation-en_US
Ign http://us.archive.ubuntu.com quantal/main Translation-en
Ign http://us.archive.ubuntu.com quantal/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com quantal/multiverse Translation-en
Ign http://us.archive.ubuntu.com quantal/restricted Translation-en_US
Ign http://us.archive.ubuntu.com quantal/restricted Translation-en
Ign http://us.archive.ubuntu.com quantal/universe Translation-en_US
Ign http://us.archive.ubuntu.com quantal/universe Translation-en
Err http://us.archive.ubuntu.com quantal-updates/main Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/restricted Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/universe Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/multiverse Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/main i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/restricted i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/universe i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-updates/multiverse i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Ign http://us.archive.ubuntu.com quantal-updates/main Translation-en_US
Ign http://us.archive.ubuntu.com quantal-updates/main Translation-en
Ign http://us.archive.ubuntu.com quantal-updates/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com quantal-updates/multiverse Translation-en
Ign http://us.archive.ubuntu.com quantal-updates/restricted Translation-en_US
Ign http://us.archive.ubuntu.com quantal-updates/restricted Translation-en
Ign http://us.archive.ubuntu.com quantal-updates/universe Translation-en_US
Ign http://us.archive.ubuntu.com quantal-updates/universe Translation-en
Err http://us.archive.ubuntu.com quantal-backports/main Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/restricted Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/universe Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/multiverse Sources
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/main i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/restricted i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/universe i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-backports/multiverse i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Ign http://us.archive.ubuntu.com quantal-backports/main Translation-en_US
Ign http://us.archive.ubuntu.com quantal-backports/main Translation-en
Ign http://us.archive.ubuntu.com quantal-backports/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com quantal-backports/multiverse Translation-en
Ign http://us.archive.ubuntu.com quantal-backports/restricted Translation-en_US
Ign http://us.archive.ubuntu.com quantal-backports/restricted Translation-en
Ign http://us.archive.ubuntu.com quantal-backports/universe Translation-en_US
Ign http://us.archive.ubuntu.com quantal-backports/universe Translation-en
Err http://us.archive.ubuntu.com quantal-proposed/restricted i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-proposed/main i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-proposed/multiverse i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Err http://us.archive.ubuntu.com quantal-proposed/universe i386 Packages
404 Not Found [IP: 91.189.91.14 80]
Ign http://us.archive.ubuntu.com quantal-proposed/main Translation-en_US
Ign http://us.archive.ubuntu.com quantal-proposed/main Translation-en
Ign http://us.archive.ubuntu.com quantal-proposed/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com quantal-proposed/multiverse Translation-en
Ign http://us.archive.ubuntu.com quantal-proposed/restricted Translation-en_US
Ign http://us.archive.ubuntu.com quantal-proposed/restricted Translation-en
Ign http://us.archive.ubuntu.com quantal-proposed/universe Translation-en_US
Ign http://us.archive.ubuntu.com quantal-proposed/universe Translation-en
Fetched 104 kB in 1min 56s (892 B/s)
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/main/source/Sources 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/restricted/source/Sources 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/universe/source/Sources 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/multiverse/source/Sources 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/main/binary-i386/Packages 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/universe/binary-i386/Packages 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.92.201 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/main/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/restricted/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/universe/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/multiverse/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/main/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/universe/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/main/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/restricted/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/universe/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/multiverse/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/main/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/universe/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-updates/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/main/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/restricted/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/universe/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/multiverse/source/Sources 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/main/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/universe/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-backports/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-proposed/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-proposed/main/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-proposed/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/quantal-proposed/universe/binary-i386/Packages 404 Not Found [IP: 91.189.91.14 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
Then I tried to re-install Okular but again getting same errors. I have tried changing software source to Main Server and also enabled authentication for third party software sources but still no progress.
