Help ! Arduino uno, xbee shield and wifi bee don't work together

Hi All,

I have Arduino uno, xbee shield ( http://www.seeedstudio.com/wiki/index.php?title=XBee®_Shield ), and wifi bee ( http://www.seeedstudio.com/wiki/index.php?title=Wifi_Bee ) .
Their hardware interface fit perfect (plug xbee shield on uno, and wifi bee on shield). But I cannot get it works.
I tried the codes in their document, but it cannot connect to any wifi network. I checked all parameters, they should have no problem.
Anyone has tried uno+xbee shiled+wifi bee ? I am newbie to arduino, anyone can tell me if this design is feesible ?
Appreciate if any body can help.

Thanks.