This represented over an hour of my life.
After upgrading to Lubuntu 14.04 LTS on my Lenovo Thinkpad X100E, I was unable to enable the wifi adapter.
In a terminal window "rfkill list" showed that wlan0 was soft-blocked. Enabling it using rfkill did not solve my problem as the UI would continue to show wifi as disabled.
Clicking on nm-applet would continue to show "Wifi disabled".
After over an hour of searching around the solution presented itself.
Right click on nm-applet and click on the Enable Wifi item on /that/ menu. If you left click, "Enable Wifi" is greyed out. If you right click, a different menu is presented with a working "Enable Wifi" item.