backend_helper.py crashed with DBusException in call_blocking(): com.ubuntu.SoftwareProperties.PermissionDeniedByPolicy: com.ubuntu.softwareproperties.applychanges

oneiric install, dist-upgraded to precise, and dist-upgraded to current today, trying to login with unity (3d), I get this failure, and no panel. I suspect that those two are not related, and that the unity panel issue could be pebcak.

ProblemType: Crash
DistroRelease: Ubuntu 12.04
Package: update-notifier-common 0.118.1ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-15.24-generic 3.2.5
Uname: Linux 3.2.0-15-generic x86_64
ApportVersion: 1.91-0ubuntu1
Architecture: amd64
Date: Sun Feb 12 15:07:30 2012
ExecutablePath: /usr/lib/update-notifier/backend_helper.py
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111011)
InterpreterPath: /usr/bin/python2.7
PackageArchitecture: all
ProcCmdline: /usr/bin/python /usr/lib/update-notifier/backend_helper.py add_cdrom /media/Ubuntu\ 12.04\ LTS\ amd64
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
PythonArgs: ['/usr/lib/update-notifier/backend_helper.py', 'add_cdrom', '/media/Ubuntu 12.04 LTS amd64']
SourcePackage: update-notifier
Title: backend_helper.py crashed with DBusException in call_blocking(): com.ubuntu.SoftwareProperties.PermissionDeniedByPolicy: com.ubuntu.softwareproperties.applychanges
UpgradeStatus: Upgraded to precise on 2012-02-12 (0 days ago)
UserGroups: adm cdrom
modified.conffile..etc.update.motd.d.90.updates.available: [deleted]
modified.conffile..etc.update.motd.d.98.reboot.required: [deleted]