Could not calculate the upgrade

[Said Bakr]

There are three causes of this problem regarded in the error message:

* Upgrading to a pre-release version of Ubuntu
* Running the current pre-release version of Ubuntu
* Unofficial software packages not provided by Ubuntu

I have not the first two causes, but I have the third. However, it is supposed that the installer temporarily cancel any third party packages in the previous step, so this cause should not be available.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
ProcVersionSignature: Ubuntu 4.4.0-134.160-generic 4.4.140
Uname: Linux 4.4.0-134-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sun Aug 26 02:19:37 2018
InstallationDate: Installed on 2017-04-29 (483 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-08-26 (0 days ago)

[Brian Murray (brian-murray)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The error that you are a reporting is a conflict between packages from the official Ubuntu archive and packages from a PPA. To resolve this situation please deactivate PPAs using the tool 'ppa-purge' which is provided by the ppa-purge package. Then try performing the release upgrade again. Thanks in advance!

[Said Bakr (said-fox)]

It is impossible to do that. I have many PPAs and ppa-purge need to specify each one.