One day I rebooted my laptop and found me working with a system with no network devices managed. NetworkManager icon was gone.
So no network at all!
It turned out, that the libnss3.so wasn’t available anymore.
The following commands made it back working (needed a wired network)
sudo service network-interface restart INTERFACE=eth0
sudo apt-get install –reinstall libnss3:i386 libnss3
The first command starts the wired network without network-manager. The second reinstalls the missing libnss3.so on my x64 system. On a x32 system, the libnss3:i386 can be removed but can ignored too.