Error while running the vision_opencv package

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hello i am new with image processing along ROS i have downloaded the vision_opencv package available on ros http://wiki.ros.org/vision_opencv while i launch the pong.launch file i receive an error that is.

ERROR 1461875334.123167512: Unable to convert '8UC1' image for display: 'cv_bridge.cvtColorForDisplay() while trying to convert image from '8UC1' to 'mono8' an exception was thrown ([8UC1] is not a color format. but [mono8] is. The conversion does not make sense)'

i dont know what it means can anyone help me please i need to do image processing in my fyp and i really need help