wlan0 on my laptop freeze my system

[jerry]

Hi,

I'm running 8 stable and I found the system freeze twice so long.
when i try ifconfig wlan0 destroy , the system hang up and freeze, Or I
  try /etc/rc.d/netif restart, the same thing happend.
I think the system freeze is because the interface wlan0, I had see the 
interface wlan0 would disappear itself!! and I saw "ioctl(SIOCGIFFLAGS) 
on wlan0: " message.
I can not found any useful info for that,but i got some strange messages 
from dmesg:

Feb 25 13:48:00 jerry wpa_supplicant[438]: CTRL-EVENT-SCAN-RESULTS
Feb 25 13:50:22 jerry kernel: arp: 00:21:00:3c:9e:f8 is using my IP 
address 192.168.1.2 on wlan0!
Feb 25 13:53:02 jerry wpa_supplicant[438]: CTRL-EVENT-SCAN-RESULTS
Feb 25 13:55:22 jerry kernel: arp: 00:21:00:3c:9e:f8 is using my IP 
address 192.168.1.2 on wlan0!
Feb 25 13:58:04 jerry wpa_supplicant[438]: CTRL-EVENT-SCAN-RESULTS
Feb 25 14:03:07 jerry wpa_supplicant[438]: CTRL-EVENT-SCAN-RESULTS
Feb 25 14:04:26 jerry wpa_supplicant[438]: Failed to disable WPA in the 
driver.
Feb 25 14:04:27 jerry kernel: wlan0: link state changed to DOWN
Feb 25 14:04:26 jerry dhclient[1580]: receive_packet failed on wlan0: 
Device not configured
Feb 25 14:04:26 jerry dhclient[1580]: ioctl(SIOCGIFFLAGS) on wlan0: 
Operation not permitted
Feb 25 14:04:26 jerry dhclient[1580]: Interface wlan0 no longer appears 
valid.
Feb 25 14:04:26 jerry dhclient[1580]: No live interfaces to poll on - 
exiting.
Feb 25 14:04:26 jerry dhclient[1580]: exiting.
Feb 25 14:04:26 jerry dhclient[1491]: connection closed
Feb 25 14:04:26 jerry dhclient[1491]: exiting.

-----------
more info
pciconf -lv:
ath0 at pci0:2:0:0:        class=0x020000 card=0x0035168c chip=0x001c168c 
rev=0x01 hdr=0x00
     vendor     = 'Atheros Communications Inc.'
     device     = 
'HDAUDIOFUNC_01&VEN_1095&DEV_1392&SUBSYS_10280242&REV_1000 
(USBVID_147E&PID_20165&B71A446&0&1)'
     class      = network
     subclass   = ethernet


$ dmesg| grep ath
ath0: <Atheros 5424/2424> mem 0xfd9f0000-0xfd9fffff irq 17 at device 0.0 
on pci2
ath0: [ITHREAD]
ath0: AR2425 mac 14.2 RF5424 phy 7.0

#rc.conf
wlans_ath0="wlan0"
ifconfig_wlan0="WPA DHCP"