Pelo que eu vejo, isso foi uma falha temporária no sistema de pacotes - então deve estar tudo bem agora.
Atualize seu computador (conforme descrito nesta pergunta: Como faço para atualizar o Ubuntu? ) e tente novamente.
Assim que eu pressionar Instalar, recebo:
Package dependencies cannot be resolved
This error could be caused by required additional software packages which are missing or not installable. Furthermore there could be a conflict between software packages which are not allowed to be installed at the same time.
Details
The following packages have unmet dependencies:
liferea: Depends: libatk1.0-0 (>= 1.12.4) but 2.0.0-0ubuntu1 is to be installed
Depends: libc6 (>= 2.7) but 2.13-0ubuntu13 is to be installed
Depends: libfontconfig1 (>= 2.8.0) but 2.8.0-2.1ubuntu3 is to be installed
Depends: libfreetype6 (>= 2.2.1) but 2.4.4-1ubuntu2.1 is to be installed
Depends: libgconf2-4 (>= 2.31.1) but 2.32.2-0ubuntu2 is to be installed
Depends: libgdk-pixbuf2.0-0 (>= 2.22.0) but 2.23.3-0ubuntu1 is to be installed
Depends: libglade2-0 (>= 1:2.6.1) but 1:2.6.4-1build1 is to be installed
Depends: libglib2.0-0 (>= 2.24.0) but 2.28.6-0ubuntu1 is to be installed
Depends: libgtk2.0-0 (>= 2.18.0) but 2.24.4-0ubuntu2 is to be installed
Depends: libice6 (>= 1:1.0.0) but 2:1.0.7-1ubuntu1 is to be installed
Depends: libnotify1-gtk2.10 but it is a virtual package
Depends: libpango1.0-0 (>= 1.14.0) but 1.28.4-0ubuntu1 is to be installed
Depends: libsoup2.4-1 (>= 2.26.1) but 2.34.0-0ubuntu1 is to be installed
Depends: libsqlite3-0 (>= 3.7.3) but 3.7.4-2ubuntu5 is to be installed
Depends: libunity4 (>= 3.4.6) but 3.8.4-0ubuntu1 is to be installed
Depends: libxml2 (>= 2.7.4) but 2.7.8.dfsg-2ubuntu0.1 is to be installed
Depends: gconf2 (>= 2.28.1-2) but 2.32.2-0ubuntu2 is to be installed
Depends: liferea-data (= 1.6.4-1ubuntu7) but 1.6.5-1~mmwkt1 is to be installed
Pelo que eu vejo, isso foi uma falha temporária no sistema de pacotes - então deve estar tudo bem agora.
Atualize seu computador (conforme descrito nesta pergunta: Como faço para atualizar o Ubuntu? ) e tente novamente.
Se você tiver esse tipo de problema, a primeira coisa a fazer é executar esses dois comandos
sudo apt-get update
seguido por
sudo apt-get upgrade
Às vezes, também corro
sudo apt-get dist-upgrade
Em seguida, tente instalar