Ath9k driver causes kernel panic and system freeze on Ubuntu 11.10

After I installed Ubuntu 11.10. I tried bridging eth0 and wlan0 with this script:

#####################################
#!/bin/bash

service network-manager stop
ifconfig eth0 0.0.0.0
ifconfig eth0 up

ifconfig wlan0 0.0.0.0
ifconfig wlan0 up

brctl addbr br0
hostapd -dd /etc/hostapd/hostapd.conf > /var/log/hostapd.log &
sleep 5
brctl addif br0 eth0
brctl addif br0 wlan0

ifconfig br0 192.168.1.15 netmask 255.255.255.0
ifconfig br0 up
route add default gw 192.168.1.1

#########################

And it showed up this error:

l2_packet_receive - recvfrom: Network is down
device wlan0 is already a member of a bridge; can't enslave it to bridge br0.

I have used same scripts on earlier Ubuntu versions; but there was no such error.

Apart from that error, after enabling the bridge, the moment another device tried to connect to it, the system freezes. I ran same script by logging to CLI (alt + f5), then when the freeze happens, error message kept on scrolling on screen (so fast that I could not read anything).

I tried loading 2.6.38 kernel, then also the first mentioned errors showed up, but system did not freeze and the bridge (access point mode) worked fine.