ubuntu-minimal package not found anymore during upgrade to ubuntu 11.10

[James Uffindell]

While upgrading to ubuntu 11.10 the updater failed with the following message, instead of completing upgrade:

After your package information was updated the essential package 'ubuntu-minimal' can not be found anymore.
This indicates a serious error, please report this bug using the command 'ubuntu-bug update-manager' in a terminal and include the files in /var/log/dist-upgrade/ in the bug report.

$lsb_release -rd
Description: Ubuntu 11.04
Release: 11.04

$ apt-cache policy update-manager
update-manager:
  Installed: 1:0.150.3
  Candidate: 1:0.150.3
  Version table:
 *** 1:0.150.3 0
        500 http://gb.archive.ubuntu.com/ubuntu/ natty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.150 0
        500 http://gb.archive.ubuntu.com/ubuntu/ natty/main amd64 Packages

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: update-manager 1:0.150.3
ProcVersionSignature: Ubuntu 2.6.38-11.50-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Thu Oct 13 19:43:19 2011
GConfNonDefault:
 /apps/update-manager/check_new_release_ignore=
 /apps/update-manager/first_run=false
 /apps/update-manager/window_size=(600,600)
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB:en
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: Upgraded to natty on 2011-10-13 (0 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Walter Garcia-Fontes (walter-garcia)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug NUMBER, so it 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. Feel free to continue to report any other bugs you may find.

[Walter Garcia-Fontes (walter-garcia)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 873468 , so it 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. Feel free to continue to report any other bugs you may find.