Windows Phone , Getting Debugg Error while saving an image to media Gallery

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C#

WinMobile

Visual-Studio

Mobile

, +

hi,
I am making a Windows Phone Application where i need to save a picture to gallery. I am using the following code. the imgview is the image
But I am getting an Debugg error at

var picture = mediaLibrary.SavePicture(fileName, stream);

. the filename which i am passing is correct. Do i need to add eny more assemblies or dll files to make that .. PlZ help me .

private bool SaveImageToPhotoHub(WriteableBitmap bmp)
        {

            using (var mediaLibrary = new MediaLibrary())
            {
                using (var stream = new MemoryStream())
                {
                    var fileName = string.Format("Gs{0}.jpg", Guid.NewGuid());
                    bmp.SaveJpeg(stream, bmp.PixelWidth, bmp.PixelHeight, 0, 100);
                    stream.Seek(0, SeekOrigin.Begin);
                    var picture = mediaLibrary.SavePicture(fileName, stream);
                    if (picture.Name.Contains(fileName)) return true;
                }
            }
            return false;
        }

        private void Save_Click(object sender, RoutedEventArgs e)
        {
            WriteableBitmap bmp = new WriteableBitmap(imgview, null);
            if (SaveImageToPhotoHub(bmp))
            {
                MessageBox.Show("Image Saved", "Information", MessageBoxButton.OK);
            }
            else
            {
                MessageBox.Show("Error : Image Not Saved", "Information", MessageBoxButton.OK);
            }
        }