I'm having issues since yesterday after an upgrade. GNOME session got messed up somehow and now i cannot install further upgrades nor new apps. Here is what i got from terminal after doing the recommended apt-get install -f;

(Reading database ... 166876 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)

In var/log/apt/history.log, it says:

Start-Date: 2011-05-29  17:56:16
Commandline: apt-get -f install
Upgrade: gnome-session:amd64 (3.0.1-0ubuntu1~build2, 3.0.2-0ubuntu3~natty1)
Error: Sub-process /usr/bin/dpkg returned an error code (1)
End-Date: 2011-05-29  17:56:21

No idea what all this means.