Server upgrade crashes

I ran

sudo do-release-upgrade

On my 11.10 server install to upgrade to 12.04. It initially seemed to run ok but then finished with an error. The following was seen on the console:

Fetched 305 MB in 6s (215 kB/s)

Upgrading
apport: unrecognized service
WARNING:root:unexpected target md5sum, skipping: '/usr/bin/pycompile'
Fetched 0 B in 0s (0 B/s)
FATAL -> Failed to fork.
ERROR:root:SystemError from cache.commit(): internal-error: unknown result code from InstallArchives: 100

Could not install the upgrades

The upgrade has aborted. Your system could be in an unusable state. A
recovery will run now (dpkg --configure -a).

Please report this bug in a browser at
http://bugs.launchpad.net/ubuntu/+source/update-manager/+filebug and
attach the files in /var/log/dist-upgrade/ to the bug report.
internal-error: unknown result code from InstallArchives: 100

Upgrade complete

The upgrade has completed but there were errors during the upgrade
process.

To continue please press [ENTER]