Problem with updating due to obsolete package versions.

Open a terminal and type:

sudo apt-get update && sudo apt-get upgrade
sudo apt-get autoclean
sudo apt-get autoremove

Since autoclean removes packages that are no longer available from configured software sources, you may want to move the sudo apt-get autoclean step until right after the sudo apt-get update step.

• Clean: clean clears out the local repository of retrieved package files. It removes everything but the lock file from /var/cache/apt/archives/ and /var/cache/apt/archives/partial/. When APT is used as a dselect method, clean is run automatically. Those who do not use dselect will likely want to run apt-get clean from time to time to free up disk space.

• Autoclean: Like clean, autoclean clears out the local repository of
  retrieved package files. The difference is that it only removes
  package files that can no longer be downloaded, and are largely
  useless. This allows a cache to be maintained over a long period
  without it growing out of control. The configuration option
  APT::Clean-Installed will prevent installed packages from being
  erased if it is set to off.

• Autoremove: is used to remove packages that were automatically
  installed to satisfy dependencies for some package and that are no
  longer needed.

See manpage