Could not upgrade from 14.04 LTS to 15.10

[Steve Hawker]

Steps to repeat:
1. Launch Software Updater
2. Software Updater reports software is up to date but offers 15.10
3. Click Upgrade and authenticate
4. Wily Werewolf Release Notes is displayed. Click Upgrade

Expect:
Upgrade to 15.10

Observe:
Process halts because "could not calculate the upgrade"

Info:

lsb_release -rd
Description: Ubuntu 14.04.4 LTS
Release: 14.04

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.16.0-76.98~14.04.1-generic 3.16.7-ckt27
Uname: Linux 3.16.0-76-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Thu Jun 30 19:47:34 2016
InstallationDate: Installed on 2015-06-25 (371 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-07-01 (0 days ago)
VarLogDistupgradeTermlog:

mtime.conffile..etc.update.manager.release.upgrades: 2016-06-30T19:36:58.457826

[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.