error installing Unity desktop when upgrading 14.04 to 15.05

[feral_shade]

It was accompanied by an error saying a list of packages could not be authenticated.
In the bug report description, it stated part of a file had been modified, and then displayed the release upgrade options from the Software Updater.
It was accompanied by an error stating that some third party services (or something) had to be disabled.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.16.0-57.77~14.04.1-generic 3.16.7-ckt20
Uname: Linux 3.16.0-57-generic i686
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: i386
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue Jan 5 17:55:05 2016
InstallationDate: Installed on 2015-07-23 (166 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release i386 (20150218.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-01-05 (0 days ago)
VarLogDistupgradeTermlog:

mtime.conffile..etc.update.manager.release.upgrades: 2016-01-01T07:42:42.451084

[Brian Murray (brian-murray)]

Part of the problem can be found in the following error message:

2016-01-05 17:52:07,746 DEBUG none of the '['ubuntu-desktop', 'kubuntu-desktop', 'xubuntu-core', 'xubuntu-desktop', 'ubuntustudio-desktop', 'mythbuntu-desktop', 'kubuntu-netbook', 'lubuntu-core', 'lubuntu-desktop', 'ubuntu-gnome-desktop']' meta-pkgs installed
2016-01-05 17:52:07,746 DEBUG guessing 'ubuntu-desktop' as missing meta-pkg

Please install the ubuntu-desktop meta package and try the upgrade again. Thanks in advance!