I suspect you may have the same problem i had with ath5K (the new Madwifi FOSS driver module). It doesn't work with certain Atheros wifi cards. The way around it is to blacklist ath5K and download, build and install the legacy 0.9.4 madwifi driver.
There's a thread a bit further down on it.
Ok... blacklisted ath5k by adding it to /etc/modprobe.d/blacklist , installed madwifi 0.9.4 , did modprobe ath_pci , added alias wlan0 ath_pci in /etc/modprobe.conf , all without errors.
But when I use wpa_supplicant with -Dwext I get the same error as before : "ioctl[SIOCSIWAUTH]: Operation not supported". Any ideas?