14.04->14.10 Upgrade didn't go through due to three reasons that seem shouldn't apply

[Bijan Vakili]

Tried to upgrade from 14.04 to 14.10
Changed /etc/update-manager/release-upgrades to have:
Prompt=normal
And then ran upgrade
sudo do-release-upgrade

Source: http://askubuntu.com/questions/614075/update-lubuntu-14-04-to-14-10
Got error:
"
Checking package manager
Reading package lists... Done
Building dependency tree
Reading state information... Done
Building data structures... Done

Calculating the changes

Calculating the changes

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.

Restoring original system state

Aborting
Reading package lists... Done
Building dependency tree
Reading state information... Done
Building data structures... Done
=== Command terminated with exit status 1 (Fri Jan 15 06:55:49 2016) ===

"

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-74.118-generic 3.13.11-ckt30
Uname: Linux 3.13.0-74-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Fri Jan 15 06:53:51 2016
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-01-15 (0 days ago)
modified.conffile..etc.update.manager.release.upgrades: [modified]
mtime.conffile..etc.update.manager.release.upgrades: 2016-01-15T06:51:49.046263

[Brian Murray (brian-murray)]

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 1534374, 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. Please continue to report any other bugs you may find.