Unable to stop the stream: Bad file descriptor

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This is the first time I try to prone this aspect of OpenCV: camera and video capture. So logically, there is nothing to do in the start other than trying to run and unerstand the basic examples such as this one which is the first to be published on the OpenCV official documentation.

I just did a copy/past to test1.py file and run it to get this error message:

    Traceback (most recent call last)
       File "test1.py", line 10, in <module>
          gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.error: /home/Begueradj/opencv/opencv-2.4.10/modules/imgproc/src/color.cpp:3739: error: (-215) scn == 3 || scn == 4 in function cvtColor

    Unable to stop the stream: Bad file descriptor

May be someone could clarify to me why this happened and how to resolve it ?

Thank you very much in advance.