Failed to upgrade from 14.04 to 15.04

[Paul]

The release upgrade fails with the following message.

---
Could not determine 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
--

Detailed logs attached.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
Uname: Linux 4.2.3-040203-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sat Nov 21 15:28:39 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-12-10 (346 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2015-11-21 (0 days ago)
VarLogDistupgradeTermlog:

mtime.conffile..etc.update.manager.release.upgrades: 2015-11-21T15:10:16.895504

[Ubuntu Foundations Team Bug Bot (crichton)]

Reviewing the files from your upgrade attempt you seem to have enabled the xorg-edgers-ppa. 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. Thanks.

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 1069133, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Please continue to report any other bugs you may find.
[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]