apt - Problems with 12.04 LTS to 14.04 LTS upgrade

I decided to upgrade from 12.04 LTS to 14.04 LTS. I used do-release-upgrade. Everything worked.

When I run lsb_release -a I get :

Description : Ubuntu 14.04.1 LTS
Release :     14.04
Codename :    trusty

I think at this moment, the upgrade is a success. But, I have these problems :

1. There's a loop when I try to login to my desktop session. cat ~/.xsession-errors gave me :

   
   

   Unable to get name "org.gnome.zeitgeist.datahub" on the bus!
   

   
   

   On LightDM I still see Ubuntu 12.04 LTS




2. I cannot install anything that could help me solve the problem above. When I run apt-get -f install I get :

   
   

   ...
   The following extra packages will be installed:
     ubuntu-release-upgrader-core
   The following NEW packages will be installed:
     ubuntu-release-upgrader-core
   ...
   E: Could not open file descriptor -1
   ...
   E: Sub-process /usr/bin/dpkg returned an error code (1)
   

When I try apt-get upgrade, it asks me at the end to run apt-get -f install.

(How) can this be fixed?

Update

To resolve the second issue, I proceeded this way : mv /etc/update-manager/release-upgrade /etc/update-manager/release-upgrade.back then dpkg -i --force-overwrite ubuntu-release-upgrader-core*.deb . At last, apt-get -f install worked. Now the challenge will be the desktop access.