Upgrade from 13.10 to 14.04 fails

[Gert]

I'm attempting to upgrade from 13.10 to 14.04 (I know I'm late, but I could not do it earlier), but it crashes. I disabled all repositories and PPAs except for the ubuntu standard repositories. The error says, that ubuntu was not able to calculate which system updates are available (roughly translated from German). Any help is appreciated a lot, I tried a lot and googled the internet for the past week, but was not able to find anything helpful.

The system is up to date using apt-get update and apt-get dist-upgrade

Probably most relevant output from console:
Es konnte nicht ermittelt werden, welche Systemaktualisierungen
verfügbar sind

Ein unlösbares Problem trat beim Berechnen der Aktualisierung auf.

Dies kann verursacht worden sein duch:
* 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.

Ein schwerwiegender Fehler ist aufgetreten

Bitte erstellen Sie einen Fehlerbericht und fügen Sie die Dateien
/var/log/dist-upgrade/main.log und /var/log/dist-upgrade/apt.log
hinzu. Die Systemaktualisierung wurde abgebrochen.
Ihre ursprüngliche sources.list wurde in
/etc/apt/sources.list.distUpgrade gesichert.

Traceback (most recent call last):

File "/tmp/ubuntu-release-upgrader-vs2ew8/trusty", line 10, in
<module>
sys.exit(main())

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeMain.py",
line 244, in main
if app.run():

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeController.py",
line 1827, in run
return self.fullUpgrade()

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeController.py",
line 1780, in fullUpgrade
if not self.askDistUpgrade():

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeController.py",
line 972, in askDistUpgrade
if not self.cache.distUpgrade(self._view, self.serverMode,
self._partialUpgrade):

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeCache.py",
line 214, in wrapper
res = f(*args, **kwargs)

File
"/tmp/ubuntu-release-upgrader-vs2ew8/DistUpgrade/DistUpgradeCache.py",
line 660, in distUpgrade
error_msg = unicode(e)

UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position
12: ordinal not in range(128)

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: ubuntu-release-upgrader-core 1:0.205.7
ProcVersionSignature: Ubuntu 3.11.0-26.45-generic 3.11.10.12
Uname: Linux 3.11.0-26-generic i686
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: i386
CrashDB: ubuntu
Date: Wed Sep 24 19:35:50 2014
MarkForUpload: True
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to saucy on 2014-09-24 (0 days ago)

[Launchpad Janitor (janitor)]

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

[Rolf Leggewie (r0lf)]

14.04 Trusty will be EOL in April 2024