Login fails with message 'Failed to load session "ubuntu"'

[Bruno Girin]

When trying to login to my account on a laptop running Unity 2D, login fails with a message saying 'Failed to load session "ubuntu"' and the only option is then to log out, which returns to the password screen.
This is after an apt-get dist-upgrade done today (17 Feb 2012) at 17:30 UK time.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity-2d (not installed)
ProcVersionSignature: Ubuntu 3.2.0-16.25-generic 3.2.6
Uname: Linux 3.2.0-16-generic i686
ApportVersion: 1.91-0ubuntu1
Architecture: i386
Date: Fri Feb 17 17:39:00 2012
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
ProcEnviron:
 LANGUAGE=en_GB:en
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: unity-2d
UpgradeStatus: Upgraded to precise on 2012-02-11 (5 days ago)

[Paolo Rotolo (paolorotolo)]

Thanks for reporting this bug and any supporting documentation. Since this bug has enough information provided for a developer to begin work, I'm going to mark it as confirmed and let them handle it from here. Thanks for taking the time to make Ubuntu better!

[Bruno Girin (brunogirin)]

Following this morning's updates, the error message no longer appears and the computer seems to initiate the session. However, it takes a very long time and the Unity launcher and top panel never appear resulting in a screen stuck with just the background image on it.

[Albert Astals Cid (aacid)]

Can you confirm if you have gnome-session 3.2.1-0ubuntu5 installed?

[Bruno Girin (brunogirin)]

Albert: I can confirm that I do have gnome-session 3.2.1-0ubuntu5 installed. If you can give me pointers as to how I can debug this, I'm happy to install anything on that machine to find the root cause of the problem.

[Michał Sawicz (saviq)]

Is it really saying that the session name is "ubuntu" and not "ubuntu-2d"? If so, it has nothing to do with unity-2d. To get more info, please check out ~/.xsession-errors.

[Bruno Girin (brunogirin)]

Hi Michał, sorry for badly reporting it. I've attached the .xsession-errors file, which does show that something's not quite right. What package should I move it to?

[kenorb (kenorb)]

Related:
https://bugs.launchpad.net/ubuntu/+source/unity-2d/+bug/959543
http://askubuntu.com/questions/74677/why-do-i-get-the-error-message-failed-to-load-session-ubuntu-2d