[Bug 1791846] [NEW] Can't upgrade to 18.04 from 16.04

[Bala]

Public bug reported:


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

Aborting
Reading package lists... Done    
Building dependency tree          
Reading state information... Done

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.12
ProcVersionSignature: hostname 4.4.0-135.161-generic 4.4.140
Uname: Linux 4.4.0-135-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon Sep 10 19:02:50 2018
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2018-09-10 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2018-09-10T17:31:46.460369

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


** Tags: amd64 apport-bug dist-upgrade third-party-packages xenial

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https://bugs.launchpad.net/bugs/1791846

Title:
  Can't upgrade to 18.04 from 16.04

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

Bug description:
  
  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

  Aborting
  Reading package lists... Done    
  Building dependency tree          
  Reading state information... Done

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.12
  ProcVersionSignature: hostname 4.4.0-135.161-generic 4.4.140
  Uname: Linux 4.4.0-135-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Mon Sep 10 19:02:50 2018
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2018-09-10 (0 days ago)
  mtime.conffile..etc.update-manager.release-upgrades: 2018-09-10T17:31:46.460369

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