No display on rviz screen

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i followed urdf tutorials under ros documentation and ran this:

roslaunch urdf_tutorial display.launch model:=06-flexible.urdf gui:=True

As a result rviz opens and it's visualizer is pitch black. I also checked RobotModel option in add in lower left corner. I then tried changing fixed and reference frame to base link. But robot is still nowhere to be seen. There is still this big black thing in 3D model. Please help. I have ROS groovy on Ubuntu 12.04.