4. Check loaded kernel modules

# lsmod
Module Size Used by
wlan_ccmp 6528 3
fglrx 376012 0
lp 7840 0
wlan_xauth 1536 0
wlan_tkip 10368 0
wlan_scan_sta 10496 1
ath_pci 74660 0
ath_rate_sample 9600 1 ath_pci
wlan 153820 7 wlan_ccmp,wlan_xauth,wlan_tkip,wlan_scan_sta,ath_pci,ath_rate_sample
ath_hal 189392 3 ath_pci,ath_rate_sample

4.1 load kernel modules in needed

if not all modules are loaded, especially wlan_xauth and wlan_tkip, try

# modprobe wlan_xauth
# modprobe wlan_tkip