[Bug 1531497] Re: unable to upgrade from ubuntu 14.04 to ubuntu 15.04 " unable to calculate upgrade"

[Brian Murray]

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: New => Confirmed

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https://bugs.launchpad.net/bugs/1531497

Title:
  unable to upgrade from ubuntu 14.04 to ubuntu 15.04 " unable to
  calculate upgrade"

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

Bug description:
  At present using Ubuntu 14.04. When the software upgrade prompted that the new release 15.04 is available, I requested for the upgrade. After initial fetching of the files the following error message appeared 
  "Calculating the changes
    Calculating the changes

  and then says:
  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 ubun...

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: ubuntu-release-upgrader-core 1:0.220.8
  ProcVersionSignature: Ubuntu 3.13.0-74.118-generic 3.13.11-ckt30
  Uname: Linux 3.13.0-74-generic x86_64
  NonfreeKernelModules: wl
  ApportVersion: 2.14.1-0ubuntu3.19
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Wed Jan  6 16:50:50 2016
  InstallationDate: Installed on 2015-02-01 (339 days ago)
  InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to trusty on 2016-01-06 (0 days ago)
  VarLogDistupgradeTermlog:
   
  mtime.conffile..etc.update.manager.release.upgrades: 2016-01-02T16:16:30.094879

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