upgrade to 16.04 could not calculate the upgrade error

[Francesco Paul]

When upgrading from 15.10 to 16.04 went ok until we got the could not calculate the upgrade error message.

I read if there are unofficial software packages it could be the problem. How would I know what packages are unofficial and how exactly would I remove them?

Long time Ubuntu user over 7 years if that helps.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.10.14.4
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic i686
ApportVersion: 2.19.1-0ubuntu5
Architecture: i386
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Thu Apr 21 17:02:46 2016
InstallationDate: Installed on 2016-02-25 (55 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release i386 (20150422)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to wily on 2016-04-21 (0 days ago)
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Carlos L. Torres (carlos-torres)]

Removing package xserver-xorg-video-nouveau fixed this for me.

[Brian Murray (brian-murray)]

Reviewing the files from your upgrade attempt you seem to have enabled a PPA that provides Xorg packages. This will prevent the upgrade as that PPA contains different versions of packages essential to Ubuntu. The page, https://launchpad.net/~xorg-edgers/+archive/ppa, contains details on to how to revert to the official Xorg packages for the xorg-edgers PPA. Instructions for reverting to official Xorg packages should be similar for the PPA that you have enabled.