OpenCV camera_calibration sample. No input found.

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Hi,

I'm trying to use the camera_calibration sample file of openCV. It compiles without errors, but for whatever reason the program is not working because the camera is not found.

Input does not exist: Invalid Input detected. Application stopping.

The code of the sample file that generates this error is:

    Settings s;
const string inputSettingsFile = argc > 1 ? argv[1] : "default.xml";
FileStorage fs(inputSettingsFile, FileStorage::READ); // Read the settings
if (!fs.isOpened())
{
    cout << "Could not open the configuration file: \"" << inputSettingsFile << "\"" << endl;
    return -1;
}
fs["Settings"] >> s;
fs.release();                                         // close Settings file
                                                      //! [file_read]

                                                      //FileStorage fout("settings.yml", FileStorage::WRITE); // write config as YAML
                                                      //fout << "Settings" << s;

if (!s.goodInput)
{
    cout << "Invalid input detected. Application stopping. " << endl;
    return -1;
}

The XML file looke like this:

<?xml version="1.0"?>
<opencv_storage>
<Settings>
 <!-- Number of inner corners per a item row and column. (square, circle) -->
 <BoardSize_Width> 7</BoardSize_Width>
 <BoardSize_Height>5</BoardSize_Height>
   <!-- The size of a square in some user defined metric system (pixel, millimeter)-->
 <Square_Size>50</Square_Size>
     <!-- The type of input used for camera calibration. One of: CHESSBOARD CIRCLES_GRID ASYMMETRIC_CIRCLES_GRID -->
 <Calibrate_Pattern>"CHESSBOARD"</Calibrate_Pattern>
   <!-- The input to use for calibration.
        To use an input camera -> give the ID of the camera, like "1"
        To use an input video  -> give the path of the input video, like "/tmp/x.avi"
        To use an image list   -> give the path to the XML or YAML file containing the list of the images, like "/tmp/circles_list.xml"
        -->
 <Input>1

   </Input>

The camera is found in all other programs. So the camera input is not the problem.

What could cause this error?