Unable to upgrade from Ubuntu 12.04 LTS to 14.04 LTS

[David Nuttall]

While calculating upgrade requirements, Distribution Upgrade stopped with a dialog that read:
Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This can be caused by:
 * Upgrading to a pre-release version of Ubuntu
 * Running the current pre-release version of Ubuntu
 * Unofficial software packages not provided by Ubuntu

If none of this applies, then please report this bug using the command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal.

None of that appeared to apply, so I did as instructed. I had recently installed the latest updated from Ubuntu, prior to doing this.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.19
ProcVersionSignature: Ubuntu 3.13.0-73.116~precise1-generic 3.13.11-ckt30
Uname: Linux 3.13.0-73-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.14
Architecture: amd64
Date: Wed Dec 9 13:22:21 2015
GsettingsChanges:
 com.ubuntu.update-manager check-new-release-ignore 'trusty'
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1449685242
 com.ubuntu.update-manager window-height 518
 com.ubuntu.update-manager window-width 600
InstallationMedia: Ubuntu 12.04.2 LTS "Precise Pangolin" - Release amd64 (20130213)
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_CA:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
Symptom: ubuntu-release-upgrader-core
UpgradeStatus: Upgraded to precise on 2015-12-09 (0 days ago)
VarLogDistupgradeTermlog:

[David Nuttall (danuttall)]

dist-update files:

[David Nuttall (danuttall)]

The term.log file is empty.

[David Nuttall (danuttall)]

I can't seem to upload the apt-clone_system_state.tar.gz file.

[Launchpad Janitor (janitor)]

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