I am trying to follow this tutorial :http://wiki.ros.org/rosserial_xbee/Tutorials/Example%20Network

However, when i run the command rosrun rosserialxbee setupxbee.py -C /dev/ttyUSB0 0 for configuring my xbee, i get an error saying "Failed to connect to the xbee."

i am using the sparkfun xbee explorer. WHat am i doing wrong? The xbee is conneced to /dev/ttyUSB0