I had what looks like the same problem with network-manager-openvpn (it looked like the same type of DBUS miscommunication.)
The problem went away after a complete system restart. I made no configuration file changes elsewhere.
I only mention this because many people seem to be reporting that everything starts working without explanation - it could very well be that a configuration file added/tweaked during install isn't being enacted until the next boot.
I had what looks like the same problem with network- manager- openvpn (it looked like the same type of DBUS miscommunication.)
The problem went away after a complete system restart. I made no configuration file changes elsewhere.
I only mention this because many people seem to be reporting that everything starts working without explanation - it could very well be that a configuration file added/tweaked during install isn't being enacted until the next boot.