Comment 35 for bug 50099

I am also running into this problem in Gutsy Tribe 5. I have a laptop which uses the ipw3945 wireless driver, and i use wpasupplicant through /etc/network/interfaces.

My solution (reached independently) has been to disable the udev rule entirely:
sudo mv /etc/udev/rules.d/85-ifupdown.rules /etc/udev/rules.d/85-ifupdown.rules.bak

This rule appears to invoke ifup on the wireless interface too soon, and prevents wpasupplicant from loading properly as defined in /etc/network/pre-up.d/wpasupplicant.