upgrade from kubuntu 10.10 to 11.04 fails with "invalid package information"

Binary package hint: update-manager

Hi,

I tried to upgrade an amd64 install of kubuntu 10.10 to kubuntu 11.04 this evening using kpackagekit. The upgrade fails with the message:

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

(K)Ubuntu release ('lsb_release -rd'):
Description: Ubuntu 10.10
Release: 10.10

software version information (apt-cache policy ...)

update-manager:
  Installed: 1:0.142.23
  Candidate: 1:0.142.23
  Version table:
 *** 1:0.142.23 0
        100 /var/lib/dpkg/status

kpackagekit:
  Installed: 0.6.2-0ubuntu1
  Candidate: 0.6.2-0ubuntu1
  Version table:
 *** 0.6.2-0ubuntu1 0
        100 /var/lib/dpkg/status

Expected outcome:
I expected the installation to proceed beyond the "Setting new software channels" stage to complete the installation.

What happened instead:
The message above was generated. Clicking the close button exits the installer.