By the way, this is only affects systems upgraded from 0.5. Just remove apt.conf rm -f /etc/apt/apt.conf and it should be fine. The file isn't used anymore.
Worked for me : rm -f /etc/apt/apt.conf
From mail I had this warning :
Code
CRON-APT RUN [/etc/cron-apt/config]: Sun May 3 07:35:03 CEST 2015
CRON-APT SLEEP: 925, Sun May 3 07:50:28 CEST 2015
CRON-APT ACTION: 3-download
CRON-APT LINE: /usr/bin/apt-get -o Acquire::http::Dl-Limit=25 autoclean -y
Reading package lists...
E: The value 'stable' is invalid for APT::Default-Release as such a release is not available in the sources
CRON-APT LINE: /usr/bin/apt-get -o Acquire::http::Dl-Limit=25 dist-upgrade -d -y -o APT::Get::Show-Upgraded=true
Reading package lists...
E: The value 'stable' is invalid for APT::Default-Release as such a release is not available in the sources
From the webinterface, no updates were available
I guess that only using SSH can fix it the problem ?