E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
alex@alex:~$ sudo apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following package was automatically installed and is no longer required:
  xulrunner-2.0-mozjs
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  gnome-session
Suggested packages:
  desktop-base
The following packages will be upgraded:
  gnome-session
1 upgraded, 0 newly installed, 0 to remove and 21 not upgraded.
76 not fully installed or removed.
Need to get 0 B/11.8 kB of archives.
After this operation, 8,192 B of additional disk space will be used.
Do you want to continue [Y/n]? y
(Reading database ... 250821 files and directories currently installed.)
Preparing to replace gnome-session 3.0.1-0ubuntu1~build2 (using .../gnome-session_3.0.2-0ubuntu3~natty1_all.deb) ...
Unpacking replacement gnome-session ...
dpkg: error processing /var/cache/apt/archives/gnome-session_3.0.2-0ubuntu3~natty1_all.deb (--unpack):
 trying to overwrite '/usr/share/xsessions/gnome-shell.desktop', which is also in package gnome-shell 3.0.1-0ubuntu1~build1
Errors were encountered while processing:
 /var/cache/apt/archives/gnome-session_3.0.2-0ubuntu3~natty1_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)