[Bug 1793123] Re: upgrade from 16.04 to 18.04 fails "Could not calculate the upgrade"

[Ubuntu Foundations Team Bug Bot]

** Tags added: xenial2bionic

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https://bugs.launchpad.net/bugs/1793123

Title:
  upgrade from 16.04 to 18.04 fails "Could not calculate the upgrade"

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  Dear Madam/Sir,

  thats what i get when i try to upgrade.
  I tried removing the unofficial PPAs but, it still doesnt work.
  Could you please let me know how to fix it?

  --------

  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 

  If none of this applies, then please report this bug using the 
  command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. 

  
  Restoring original system state

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.25
  ProcVersionSignature: Ubuntu 4.15.0-34.37~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-34-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Tue Sep 18 13:20:00 2018
  InstallationDate: Installed on 2017-09-27 (355 days ago)
  InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2018-09-18 (0 days ago)
  mtime.conffile..etc.update-manager.release-upgrades: 2018-09-13T15:59:18.055246

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