ubantu 10.04 with madwifi ath_pci driver hang with iperf client

Hello friends, i am dealing with very strange problem from couple of weeks
i am doing performance measurement for wireless network , i am using
ubantu 10.04 with madwifi ath_pci driver , i have connected to machine
using RF cables to form network , when i run iperf clinet for UDP and
Iperf Server on other ,my machine UDP iperf client hang with black
screen, only hard reboot is option. i am not able to progress , please
help if somebody know solution

thanks in advance

------------------------------------------------------------------------------
For Developers, A Lot Can Happen In A Second.
Boundary is the first to Know...and Tell You.
Monitor Your Applications in Ultra-Fine Resolution. Try it FREE!
http://p.sf.net/sfu/Boundary-d2dvs2