C#.net验证码问题

 

使用了无效参数。 说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.ArgumentException: 使用了无效参数。{"Parameter is not valid."}

源文件: public partial class ValidateImage : System.Web.UI.Page{    private readonly string ImagePath = "~/Images/validator.jpg";    private string sValidator = "";    private Brush[] BrushList = new Brush[32];

    private void Page_Load(object sender, System.EventArgs e)    {        ///初始化        InitBrushList();

        if (Request.Params["Validator"] != null)        {            ///获取验证字符串            sValidator = Request.Params["Validator"].ToString();        }

        ///创建Bmp位图      Bitmap bitMapImage = new System.Drawing.Bitmap(Server.MapPath(ImagePath));        Graphics graphicImage = Graphics.FromImage(bitMapImage);

        ///设置画笔的输出模式        graphicImage.SmoothingMode = SmoothingMode.AntiAlias;        ///添加文本字符串        for (int i = 0; i < sValidator.Length; i++)        {            graphicImage.DrawString(sValidator[i].ToString(),                new Font("Arial", 20, (FontStyle)CreateRandomFontStyle(GetRandomint(0, 1000))),                BrushList[GetRandomint(0, BrushList.Length - 1)],                new PointF(i * 15, GetRandomint(-5, 5)));        }

        //graphicImage.DrawString(sValidator, new Font("Arial", 20, (FontStyle)GetRandomint(0,4)),SystemBrushes.WindowText, new Point(0, 0));

        ///设置图像输出的格式        Response.ContentType = "image/jpeg";

        ///保存数据流        bitMapImage.Save(Response.OutputStream, ImageFormat.Jpeg);

        ///释放占用的资源        graphicImage.Dispose();        bitMapImage.Dispose();        Response.End();    }