I guess that you want associate your wlan0 with AP? Then you should use also "iwconfig wlan0" command.
And as for me, i recommend use "ifup" and "ifdown" scripts for reconfiguration network interfaces.
After your manipulation, did you try:
What result was?Code:airmon-ng stop mon0 (optional, if Monitor mode started earlier) airmon-ng start wlan0 airodump-ng -a mon0