[Bug 1797044] [NEW] unable to update ubuntu from 16.04 to 18.04. Error message received "An unresolvable problem occurred while calculating the upgrade."

[Valentin]

Public bug reported:

lsb_release -rd
Description:	Ubuntu 16.04.5 LTS
Release:	16.04

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
ProcVersionSignature: Ubuntu 4.15.0-36.39~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Wed Oct 10 09:49:00 2018
InstallationDate: Installed on 2016-10-07 (732 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-10-10 (0 days ago)

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug dist-upgrade xenial

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https://bugs.launchpad.net/bugs/1797044

Title:
  unable to update ubuntu from 16.04 to 18.04. Error message received
  "An unresolvable problem occurred while calculating the upgrade."

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

Bug description:
  lsb_release -rd
  Description:	Ubuntu 16.04.5 LTS
  Release:	16.04

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.25
  ProcVersionSignature: Ubuntu 4.15.0-36.39~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-36-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: XFCE
  Date: Wed Oct 10 09:49:00 2018
  InstallationDate: Installed on 2016-10-07 (732 days ago)
  InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2018-10-10 (0 days ago)

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