W:GPG error: http://ftp.de.debian.org sid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA NO_PUBKEY 8B48AD6246925553, W:Failed to fetch http://ppa.launchpad.net/ubun-tor/ppa/ubuntu/dists/precise/main/source/Sources  404  Not Found
, W:Failed to fetch http://ppa.launchpad.net/ubun-tor/ppa/ubuntu/dists/precise/main/binary-amd64/Packages  404  Not Found
, W:Failed to fetch http://ppa.launchpad.net/ubun-tor/ppa/ubuntu/dists/precise/main/binary-i386/Packages  404  Not Found
, E:Some index files failed to download. They have been ignored, or old ones used instead.

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The following packages have unmet dependencies:

skype: Depends: skype-bin but it is not installable

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software index is broken

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An unresolvable problem occurred while calculating the upgrade:
E:Unable to correct problems, you have held broken packages.

 This can be caused by:
 * Upgrading to a pre-release version of Ubuntu
 * Running the current pre-release version of Ubuntu
 * Unofficial software packages not provided by Ubuntu

This is most likely a temporary problem, please try again later