Can't change MAC address of my WAG311

[FreeBSD Daemon]

dear list,

I am operating a Netgear WAG311 (Atheros AR5212) under FBSD 5.3 Release.

I tried to change the MAC address of the device using

    root# ifconfig ath0 ether aa:bb:cc:dd:ee:ff

which changed the MAC address in the ifconfig ath0 output. But wicontrol 
-i ath0 still showed the old (original) MAC address and that MAC address 
also is being used on the network.

Trying to change the MAC address using

    root# wicontrol -i ath0 -m aa:bb:cc:dd:ee:ff

results in a

    wicontrol: SIOCSWAVELAN: Invalid Argument

error message.

Am I doing something wrong?

TIA

zheyu