Comment 4 for bug 45696

I had this happen yesterday. After killing all NetworkManager-related processes (NetworkManager, NetworkManagerDispatcher and nm-applet), and restarted them, things were back to normal. Using "/etc/init.d/netapplet restart", "/etc/init.d/networking restart" or simply killing and restarting "nm-applet" had no effect at all.

Note that it does not always happen, most of the time everything works as normal.