Can not upgrade from 14.04 to 16.04

[scippane]

After running the command

sudo do-release-upgrade

I get the following error message

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

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-93.140-generic 3.13.11-ckt39
Uname: Linux 3.13.0-93-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Sat Aug 20 18:30:22 2016
InstallationDate: Installed on 2012-10-31 (1389 days ago)
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-08-21 (0 days ago)