[Bug 1791509] [NEW] upgrade from 16.04 LTS to 18.04 LTS aborted

[fieryhydra]

Public bug reported:

I got the following error report on terminal when attempting to upgrade my 16.04 LTS version to 18.04 LTS version, when following the instructions on upgrading available on the Ubuntu website.
--------------
Could not calculate the upgrade 

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.
----------

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.25
ProcVersionSignature: Ubuntu 4.15.0-33.36~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-33-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Sun Sep  9 06:43:20 2018
InstallationDate: Installed on 2018-01-01 (250 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-09-09 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2018-09-09T06:31:53.089990

** 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/1791509

Title:
  upgrade from 16.04 LTS to 18.04 LTS aborted

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

Bug description:
  I got the following error report on terminal when attempting to upgrade my 16.04 LTS version to 18.04 LTS version, when following the instructions on upgrading available on the Ubuntu website.
  --------------
  Could not calculate the upgrade 

  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.
  ----------

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.25
  ProcVersionSignature: Ubuntu 4.15.0-33.36~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-33-generic x86_64
  NonfreeKernelModules: wl
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Sun Sep  9 06:43:20 2018
  InstallationDate: Installed on 2018-01-01 (250 days ago)
  InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2018-09-09 (0 days ago)
  mtime.conffile..etc.update-manager.release-upgrades: 2018-09-09T06:31:53.089990

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