I was able to fix it a bit.
* I had to comment out an existing eth0 connection.
* Add a new connection available for all users (which disappeared) using nm-connection-editor running as root (with sudo).
* Then restart networking with the init.d script and NetworkManager with the Upstart "restart" utility
Now I have a globally available connection.
I am forced to use DHCP, static configuration keeps on disappearing, but ok it's usable already.
I was able to fix it a bit. editor running as root (with sudo).
* I had to comment out an existing eth0 connection.
* Add a new connection available for all users (which disappeared) using nm-connection-
* Then restart networking with the init.d script and NetworkManager with the Upstart "restart" utility
Now I have a globally available connection.
I am forced to use DHCP, static configuration keeps on disappearing, but ok it's usable already.
Note: this was concerning a wired connection.