Error using openni_tracker with pr2_simulator

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I'm attempting to use the openni_tracker package in conjunction with the pr2_simulator simulation. I've followed instructions to do so from this page, here.
I complete the installation (without error) through the step to rosrun openni_tracker openni_tracker. At that point, when trying to rosrun the package, I get this error:

joe@ROS:~$ rosrun openni_tracker openni_tracker 
/home/joe/catkin_ws/src/openni_tracker/openni_tracker.xml
[ERROR] [1458319658.103197859]: InitFromXml failed: Can't create any node of the requested type!

How do I verify that openni_tracker is subscribing to the correct topic? And would that be related to the failure of the XML to load?
Any ideas?
Thank you.