[Bug 1708373] [NEW] upgrade from 16.04 to 17.04 failed "Could not calculate the upgrade"

[Jerry]

Public bug reported:

Running 16.04, trying to upgrade to 17.04. Error during the second step "Setting new software channels". Error dialog says:
```
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.
```
No idea what could cause this...

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.22
ProcVersionSignature: Ubuntu 4.4.0-87.110-generic 4.4.73
Uname: Linux 4.4.0-87-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Thu Aug  3 09:11:34 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-07-11 (387 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2017-08-03 (0 days ago)
VarLogDistupgradeTermlog:
 
mtime.conffile..etc.update-manager.release-upgrades: 2017-08-03T09:04:42.657655

** 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/1708373

Title:
  upgrade from 16.04 to 17.04 failed "Could not calculate the upgrade"

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

Bug description:
  Running 16.04, trying to upgrade to 17.04. Error during the second step "Setting new software channels". Error dialog says:
  ```
  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.
  ```
  No idea what could cause this...

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.22
  ProcVersionSignature: Ubuntu 4.4.0-87.110-generic 4.4.73
  Uname: Linux 4.4.0-87-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.10
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: XFCE
  Date: Thu Aug  3 09:11:34 2017
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2016-07-11 (387 days ago)
  InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2017-08-03 (0 days ago)
  VarLogDistupgradeTermlog:
   
  mtime.conffile..etc.update-manager.release-upgrades: 2017-08-03T09:04:42.657655

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