Could not upgrade from Ubuntu 14.04.5 LTS to 16.04

[Ravishankar R]

Get the following error:
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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.
--

I have none of these conditions mentioned in the message. I have a clean running installation of Ubuntu 14.04.5

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.10
ProcVersionSignature: Ubuntu 4.4.0-135.161~14.04.1-generic 4.4.140
Uname: Linux 4.4.0-135-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.29
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sun Sep 23 09:25:19 2018
InstallationDate: Installed on 2016-09-13 (739 days ago)
InstallationMedia: Ubuntu 14.04.5 LTS "Trusty Tahr" - Release amd64 (20160803)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2018-09-23 (0 days ago)
VarLogDistupgradeTermlog: