package unattended-upgrades 0.73ubuntu1 [modified: usr/share/unattended-upgrades/unattended-upgrade-shutdown] failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Brian]

Setting up unattended-upgrades (0.73ubuntu1) ...
update-rc.d: warning: unattended-upgrades start runlevel arguments (2 3 4 5) do not match LSB Default-Start values (none)
update-rc.d: warning: unattended-upgrades stop runlevel arguments (0 1 6) do not match LSB Default-Stop values (0 6)
Checking for running unattended-upgrades:
Traceback (most recent call last):
  File "/usr/share/unattended-upgrades/unattended-upgrade-shutdown", line 27, in <module>
    import apt_pkg
ImportError: No module named apt_pkg
invoke-rc.d: initscript unattended-upgrades, action "start" failed.
dpkg: error processing unattended-upgrades (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 unattended-upgrades
E: Sub-process /usr/bin/dpkg returned an error code (1)

ProblemType: Package
DistroRelease: Ubuntu 11.10
Package: unattended-upgrades 0.73ubuntu1 [modified: usr/share/unattended-upgrades/unattended-upgrade-shutdown]
ProcVersionSignature: Ubuntu 3.0.0-11.17-generic 3.0.4
Uname: Linux 3.0.0-11-generic i686
ApportVersion: 1.23-0ubuntu1
Architecture: i386
Date: Thu Sep 22 12:15:49 2011
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
PackageArchitecture: all
SourcePackage: unattended-upgrades
Title: package unattended-upgrades 0.73ubuntu1 [modified: usr/share/unattended-upgrades/unattended-upgrade-shutdown] failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to oneiric on 2011-09-08 (13 days ago)