Error ( A generic error occurred in GDI+)

Question

  protected void Page_Load(object sender, EventArgs e)
        {
            QRCodeEncoder encoder = new QRCodeEncoder();

            Bitmap img = encoder.Encode("http://www.markhagan.me/");

  img.Save("C:\\img.jpg", ImageFormat.Jpeg);

            QRImage.ImageUrl = "img.jpg";

        }

         Como resolver esse problema ?