Recently I ran into an issue where a new installation of Debian didn’t have NetworkManager set up correctly. Everytime I tried to use NetworkManager it had an issue with the devices not being managed. Luckily there was a man page for networkmanager.conf and its a quick fix.
All you have to do is
sudo vi /etc/NetworkManager/NetworkManager.conf
sudo service network-manager restart
And it’s fixed. Your wireless and ethernet connections will then be managed by NetworkManager. If you don’t want network manager to manage anymore you can just stop the service, or disable it at boot time by removing it from your /etc/rc[x].d/ directory where [x] corresponds to your runlevel. Enjoy!