Can't upgrade from Lubuntu 14.04.5 LTS to 16.04.1 LTS

[Mindaugas Jakutis]

Shell output:
```
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
```
To the best of my knowledge none of these apply to my system.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-96.143-generic 3.13.11-ckt39
Uname: Linux 3.13.0-96-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
Date: Fri Oct 21 20:45:05 2016
InstallationDate: Installed on 2015-11-08 (347 days ago)
InstallationMedia: Lubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-10-21 (0 days ago)

[Mindaugas Jakutis (la-mj)]

Removing gnote 'fixed' it