update-manager crashed with ImportError in /usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeQuirks.py: No module named plugincore.manager

[Hail Holy Ghost]

Hello,

I am experiencing many different problems after upgrading to Precise, or at least what I thought was precise. The Unity interface is barely functional in my opinion (I like the taskbar) so I am attempting to convert back to Gnome.

When I attempt to reinstall GNOME:

#1 The following packages have unmet dependencies:

gnome: Depends: gnome-core (= 1:3.0+6ubuntu3) but 1:3.0+6ubuntu3 is to be installed

I have been running in circles trying to get gnome reinstalled. There are so many bugs on my computer now I can't do anything.

#2 For some reason (I did NOT do this intentionally) I am running a development version of 12.10. This may be the source of my problems.

I did this:
1) sudo sed -i 's/quantal/precise/g' /etc/apt/sources.list
2) sudo apt-get update && sudo apt-get dist-upgrade
3) sudo apt-get update
4) sudo apt-get upgrade

This link http://askubuntu.com/questions/49869/how-to-roll-back-ubuntu-to-a-previous-version was not helpful.

ProblemType: Crash
DistroRelease: Ubuntu 12.10
Package: update-manager 1:0.163
ProcVersionSignature: Ubuntu 3.5.0-1.1-generic 3.5.0-rc3
Uname: Linux 3.5.0-1-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.2.3-0ubuntu6
Architecture: amd64
Date: Thu Jun 21 04:34:30 2012
DuplicateOf: https://bugs.launchpad.net/bugs/1013490
ExecutablePath: /usr/bin/update-manager
GsettingsChanges:

InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
InterpreterPath: /usr/bin/python3.2mu
PackageArchitecture: all
ProcCmdline: /usr/bin/python3.2 /usr/bin/update-manager --dist-upgrade
ProcCwd: /home/david
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
 TERM=unknown
PythonArgs: ['/usr/bin/update-manager', '--dist-upgrade']
SourcePackage: update-manager
Title: update-manager crashed with ImportError in /usr/lib/python3/dist-packages/DistUpgrade/DistUpgradeQuirks.py: No module named plugincore.manager
UpgradeStatus: Upgraded to quantal on 2012-06-21 (0 days ago)
UserGroups:

[Apport retracing service (apport)]

Thank you for taking the time to report this crash and helping to make this software better. This particular crash has already been reported and is a duplicate of bug #1013490, so is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Please continue to report any other bugs you may find.