Cant upload code to arduino mega

I have an arduino mega 1280 also i have a dfrobot mega shield on it (http://www.dfrobot.com/index.php?route=product/product&product_id=339) which support xbees chips... I put it in the xbee adafruit sells (http://www.adafruit.com/products/128). But im having a problem uploading code..

When the xbee is connected to my shield i get error messages saying that it cant load code cuz the programmer is not responding... If i remove the xbee i can upload code just fine. If i put it back up it works perfectly i just cant upload code while it is in it..

Is there a way to load code (using reg usb cable and reg arduino IDE) while the xbees is in???