wireless networking - Can't activate wlan0 in CentOS5.5

When I try to activate wlan0 in CentOS5.5, I get this:

Error for wireless request "Set Mode" (8B06) :
    SET failed on device wlan0 ; Invalid argument.

Determining IP information for wlan0...Internal network device wlan0 is not ready.
Aborting..

EDIT: I have the correct driver now, but it's still not working.