dpkg error while installing gnome-session-fallback

Question

I was trying to do sudo apt-get install gnome-session-fallback. This is the output I get:

(Reading database ... 353039 files and directories currently installed.)
Preparing to unpack .../gnome-panel-data_1%3a3.8.0-1ubuntu12.2_all.deb ...
Unpacking gnome-panel-data (1:3.8.0-1ubuntu12.2) ...
dpkg: error processing archive /var/cache/apt/archives/gnome-panel-data_1%3a3.8.0-1ubuntu12.2_all.deb (--unpack):
trying to overwrite '/usr/share/locale/mn/LC_MESSAGES', which is also in package language-selector-common 0.129.3
dpkg-deb: error: subprocess paste was killed by signal (Broken pipe)
Preparing to unpack .../gnome-applets-data_3.5.92-0ubuntu3_all.deb ...
Unpacking gnome-applets-data (3.5.92-0ubuntu3) ...
dpkg: error processing archive /var/cache/apt/archives/gnome-applets-data_3.5.92-0ubuntu3_all.deb (--unpack):
trying to overwrite '/usr/share/locale/mn/LC_MESSAGES', which is also in package language-selector-common 0.129.3
dpkg-deb: error: subprocess paste was killed by signal (Broken pipe)
Processing triggers for libglib2.0-0:i386 (2.40.2-0ubuntu1) ...
Processing triggers for libglib2.0-0:amd64 (2.40.2-0ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...
Processing triggers for gconf2 (3.2.6-0ubuntu2) ...
Errors were encountered while processing:
 /var/cache/apt/archives/gnome-panel-data_1%3a3.8.0-1ubuntu12.2_all.deb
 /var/cache/apt/archives/gnome-applets-data_3.5.92-0ubuntu3_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

I tried to upgrade and update:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
  gnome-applets : Depends: gnome-applets-data (>= 3.5) but it is not installed
             Depends: gnome-applets-data (< 3.6) but it is not installed
             Recommends: gnome-media but it is not installed
  gnome-panel : Depends: gnome-panel-data (= 1:3.8.0-1ubuntu12.2) but it is not installed
           Recommends: alacarte but it is not installed
E: Unmet dependencies. Try using -f.

hence, I tried sudo apt-get -f install and I got the same output as sudo apt-get install gnome-session-fallback. I got a prompt to report this bug in launchpad. Any solutions?

I also tried to install aptitude (or any other package) I get this:

You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 aptitude : Depends: aptitude-common (= 0.6.8.2-1ubuntu4) but it is not going to be installed
        Depends: libboost-iostreams1.54.0 but it is not going to be installed
        Depends: libcwidget3 but it is not going to be installed
        Depends: libept1.4.12 but it is not going to be installed
 gnome-applets : Depends: gnome-applets-data (>= 3.5) but it is not going to be installed
             Depends: gnome-applets-data (< 3.6) but it is not going to be installed
             Recommends: gnome-media but it is not going to be installed
 gnome-panel : Depends: gnome-panel-data (= 1:3.8.0-1ubuntu12.2) but it is not going to be installed
           Recommends: alacarte but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

Manual installation of aptitude deb file from here, gives this:

New sofware cant be installed because there is a problem with the software currently installed. Do you want to repair this porblem now? 

Clicked on repair. Package operation failed.

Answer 1

This is safe to run for unity. Although, you should always carefully review the list of packages to uninstall before you agree to make the changes as you may have some other application that uses one of these as a dependency and it may get uninstalled automatically as a result. For example, this will most likely uninstall gnome-shell.

Run the following commands:

sudo apt-get purge alacarte evolution evolution-common evolution-plugins gir1.2-panelapplet-5.0 gnome-applets gnome-applets-data gnome-flashback gnome-flashback-common gnome-media gnome-panel gnome-panel-data gnome-power-manager gnome-session-flashback indicator-applet-complete libevolution libgtkhtml-4.0-0 libgtkhtml-4.0-common libgtkhtml-editor-4.0-0 libmail-spf-perl libnetaddr-ip-perl libpanel-applet0 libpst4 libytnef0 metacity re2c sa-compile spamassassin spamc gnome-session-fallback aptitude

If that doesn't work, run this instead:

sudo dpkg -P alacarte evolution evolution-common evolution-plugins gir1.2-panelapplet-5.0 gnome-applets gnome-applets-data gnome-flashback gnome-flashback-common gnome-media gnome-panel gnome-panel-data gnome-power-manager gnome-session-flashback indicator-applet-complete libevolution libgtkhtml-4.0-0 libgtkhtml-4.0-common libgtkhtml-editor-4.0-0 libmail-spf-perl libnetaddr-ip-perl libpanel-applet0 libpst4 libytnef0 metacity re2c sa-compile spamassassin spamc gnome-session-fallback aptitude

Then, clean everything up and when you are done running the following commands, go ahead and try the installation again or file a bug report:

sudo apt-get update
sudo apt-get clean

Please post any errors.