The Fn+F5 key combination of my thinkpad X31 suddenly stopped working and kept giving an error dialog saying that: Unable to change Power State of 802.11 wireless radio.
I recalled I did change the configuration of my intel wireless 2100 3B adaptor recently and disabled a couple of protocols from its driver listing. After I enabled the "WLAN Transport" protocol as shown in the screenshot below, the Fn+F5 key worked again! It seems the hardware driver relys on WNMP to switch the power of the wireless radio.