Release upgrade from 14.04 to 14.10 fails

[FM_Kerckhof]

System upgrade from 14.04 to 14.10 on a Ubuntu desktop 14.04.1 LTS on a Dell Optiplex 760 with intel Core2 Quad Q8300 CPU and an intel 4 series integrated graphics controller (`uname -a` :`Linux systemname 3.13.0-53-generic #87-Ubuntu SMP Thu May 7 14:32:24 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux`) on which I have some problems loading the desktop interface: http://askubuntu.com/questions/548376/ubuntu-14-04-desktop-environment-does-not-load . I was hoping a release upgrade may resolve issues.

The initial process of do-release upgrade works well but after the "calculating changes" step I get the following output:

Calculating the changes
Calculating the changes
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

It is quite weird "calculating the changes" shows twice. I am upgrading from an LTS version so I don't think I am running a current pre-release version. I am upgrading to 14.10 while 15.04 is already out so I don't think I am upgrading to a pre-release version. I am unaware of unofficial software packages prohibiting upgrade nor how to check if they do.

lsb-release -rd outputs:
Description: Ubuntu 14.04.2 LTS
Release: 14.04

apt-cache policy ubuntu-release-upgrader-core yields:
ubuntu-release-upgrader-core:
  Installed: 1:0.220.7
  Candidate: 1:0.220.7
  Version table:
 *** 1:0.220.7 0
        500 http://be.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.220.2 0
        500 http://be.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.7
ProcVersionSignature: Ubuntu 3.13.0-53.87-generic 3.13.11-ckt19
Uname: Linux 3.13.0-53-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.10
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon May 11 10:49:07 2015
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2015-05-11 (0 days ago)
modified.conffile..etc.update.manager.release.upgrades: [modified]
mtime.conffile..etc.update.manager.release.upgrades: 2015-05-11T10:17:53.087470