Wep? wpa-wpa2? Have you tried WPA-WPA2? Only WEP doesn't work? Both encryption don't work?
Need more info..Certainly WEp has issues on ath9k module sometimes even upgrading compat-wireless.
You might want to upgrade to BT5r3 : ----> http://www.backtrack-linux.org/backt...acktrack-5-r3/
Also try this:
modprobe ath9k nohwcrypt=1
Try to connect...