I've noticed the following issue with my Ubuntu 12.04 installation. After some time while the laptop is working the network manager becomes not responsive at all. For example: I can see the available wireless networks, but I can't disconnect from the current SSID and connect to another SSID, or I can't connect using my USB 3G modem.
Loging out and than back loging into the session solve this. Any idea?
P.S. During all the time when I'm connected, I don't have issues with the connectivity.