What could be the cause of reboot hang on iptables script with niu driver interface up in RHL6.0 systems

Hi,

Some of my Redhat 6.0 systems always have reboot hang problem on 
iptables script with niu driver interface up. After adding some debug 
stuff, I can see the system alway hang on " modprobe -r xt_state". What 
could be the cause of it? Does niu driver need to handle some 
calls/ioctls that currently not implemented in the niu driver?

Thanks,
Joyce