Could not calculate the upgrade

[Emil]

hi,
it shows (box) when trying to update my 14.04 to 16.
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.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.9
ProcVersionSignature: Ubuntu 3.13.0-119.166-generic 3.13.11-ckt39
Uname: Linux 3.13.0-119-generic i686
ApportVersion: 2.14.1-0ubuntu3.24
Architecture: i386
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon Jun 12 15:27:55 2017
InstallationDate: Installed on 2016-03-16 (452 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release i386 (20140722.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2017-06-12 (0 days ago)
VarLogDistupgradeTermlog: