Luis,
Unload/load modules of ar9271 in sequence:
1. firmware loaded failed
modprobe ath9k_htc -r
modprobe ath_hif_usb -r
modprobe ath9k_htc
modprobe ath_hif_usb
2. system hangs
modprobe ath_hif_usb -r
modprobe ath9k_htc -r
modprobe ath9k_htc
modprobe ath_hif_usb
I spent a weekend and could not see why.
---henry