could not calculate upgrade while upgrading to 18.04

[Andrew Wang]

While trying to upgrade to Ubuntu 18.04, I get this error message:

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

 This was likely caused by:
 * Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.29
ProcVersionSignature: Ubuntu 4.4.0-177.207-generic 4.4.214
Uname: Linux 4.4.0-177-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sun Apr 19 11:29:04 2020
InstallationDate: Installed on 2018-06-17 (672 days ago)
InstallationMedia: Ubuntu-Server 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.8)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2020-04-19 (0 days ago)
VarLogDistupgradeTermlog:

[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 package version numbers greater than the release to which you are upgrading. You can revert the PPA by installing the ppa-purge package from the official Ubuntu archive and then running 'sudo ppa-purge oibaf'. After that you try upgrading and again and if it still fails open a new bug report. Thanks and good luck!