For a while now I've been trying to connect to my AP with a spoofed mac via macchanger. This is what I do;

Code:
bt ~# ifconfig wlan0 down
bt ~# macchanger -A wlan0

Then I get assigned a random MAC

bt ~# ifconfig wlan0 up
bt ~# iwconfig wlan0 mode managed key [WEP KEY]
bt ~# iwconfig wlan0 essid [ESSID]
bt ~# dhclient wlan0

 This is where it goes wrong...
I can't get assigned an IP via the AP

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wmaster0: unknown hardware address type 801
wmaster0: unknown hardware address type 801
Listening on LPF/wlan0/[My spoofed MAC]
Sending on LPF/wlan0/[My spoofed MAC]
Sending on Socket/fallback
DHCPREQUEST on wlan0 to 255.255.255.255 port 67
DHCPNAK from 192.168.1.1
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
receive _packet failed on wlan0: Network is down
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 9
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 13
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 14
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 9
No DHCPOFFERS received.
No working leases in persistant database - sleeping
bt ~#
However if I go through the procedure again minus the macchanger command I can connect fine.

I use the iwl3945 drivers with the Intel Pro chipset. I've tried loading the ipwraw drivers but it doesn't like that too.

Am I doing something wrong or is my card an issue?

Thanks.