upgrade 14.04 LTS to 16.04.1 LTS impossible

[matze]

System offers to install 16.04.1 LTS over 14.04. After several minutes the message "unsolvable problem" appears

Es konnte nicht ermittelt werden, welche Systemaktualisierungen verfügbar sind

Ein unlösbares Problem trat beim Ermitteln der Systemaktualisierung auf.

 Dies kann verursacht worden sein durch:
 * Aktualisieren auf eine Vorabversion von Ubuntu
 * Verwendung der aktuellen Vorabversion von Ubuntu
 * Inoffizielle Softwarepakete, die nicht von Ubuntu bereitgestellt wurden

Falls nichts von dem zutrifft, melden Sie diesen Fehler bitte, indem Sie den Befehl »ubuntu-bug ubuntu-release-upgrader-core« in einem Terminal ausführen.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-core 1:0.220.8
ProcVersionSignature: Ubuntu 3.13.0-93.140-generic 3.13.11-ckt39
Uname: Linux 3.13.0-93-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: GNOME
Date: Sun Jul 31 17:25:24 2016
InstallationDate: Installed on 2013-10-08 (1026 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2016-07-31 (0 days ago)
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Wolfgang Fahl (wf-bitplan)]

See https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1486162. The bug is in the message that doesnot give any hints on how to resolve this. E.g. looking in /var/log/dist-upgrade log files or using ppa-purge see http://askubuntu.com/questions/307/how-can-ppas-be-removed

[Wolfgang Fahl (wf-bitplan)]

see http://www.vdr-portal.de/board60-linux/board14-betriebssystem/board68-debian-und-derivate/122243-do-release-upgrade-funktioniert-nicht/

[Wolfgang Fahl (wf-bitplan)]

https://blog.mcdope.org/2014/04/18/ubuntu-14-04-upgrade-unloesbares-problem/

[Wolfgang Fahl (wf-bitplan)]

in my case
apt-get remove ros-indigo-ros-base
apt-get autoremove
root@capri:/etc/apt/sources.list.d# mkdir /home/wf/sources.list
root@capri:/etc/apt/sources.list.d# mv ros* /home/wf/sources.list/

seems to have been the necessary step so grep "Broken" /var/log/dist-upgrade/<date>/apt.log was the first step in finding this out. The do-release-upgrade script should IMHO point to a wiki entry where these issues are discussed so that people can discuss there personal PPA situation and fixes.