Extremely sorry if I am posting in an area where I am not supposed to. The last thing I want to do is upset mods or members. My question is probably a simple solution but I can't seem to figure it out. I have a backtrack live USB that I load. Once in the GUI I open the shell and change the mac as follows

ifconfig wlan0 down
ifconfig wlan0 hw ether XX:XX:XX:XX:XX:XX
ifconfig wlan0 up
then i use,
after that i try to connect to an access point and I always get stuck at "Obtaining IP address"

When I just proceed without changing the MAC everything works fine as far as connecting to the AP. Has anyone else experienced this?