Comment 51 for bug 207446

I, too, can confirm that this workaround works. Thanks all!

cirobr,
You need to remove or disable Network Manager and use manual setup via a 'wpa_supplicant.conf' configuration file in order for the /etc/network/interfaces mod to work. There are detailed How-To's and User Guides on the use of WPA_Supplicant on the Ubuntu website. Otherwise, with Network Manager running, you would need to execute the two command lines Chri provided above each and every time Ubuntu starts up and you want to establish a WPA wireless connection. HTH...