face detection using emgucv library.

I am doing face detection using haar detector from emgu cv open library.
Using the language C#.

public Form1()
{
    InitializeComponent();
    try
    {
        haar = new HaarCascade("C:\\Program Files\\emgucv2.1.0.793\\opencv\\data\\haarcascades\\haarcascade_frontalface_alt_tree.xml");
        
        capture = new Capture(0);
    }
    catch
    {
    }
}

private void timer1_Tick(object sender, EventArgs e)
{
    {
        Image<bgr,> image = capture.QueryFrame();
    Bitmap original = image.ToBitmap(pictureBox1.Width,pictureBox1.Height);

It is giving error at run time.
It does not show image in the picture box when it runs and gives null reference exception in line:

Image<bgr,> image = capture.QueryFrame();

I have used breakpoints to detect errors, it is going to the Haar line but it not entering in capture line capture= new capture(0).

Can anyone tell me the error why image is not been captured in picture box at run time?
I tried this using emgucv liberary in win XP as well as window 7.

Tags: C#, EMGUCV