大家帮我看看为什么不对

[rainvoice_zj]

这是我刚写的一个验证码程序,不知为什么,最后一行代码最是报错,希望大哥大姐们能帮帮小弟我.谢谢谢了.

private void Page_Load(object sender, System.EventArgs e)
{
Bitmap newBitmap = new Bitmap(36,16,PixelFormat.Format32bppArgb);
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(newBitmap);
g.FillRectangle(new SolidBrush(Color.White),new Rectangle(0,0,36,16));
System.Drawing.Font textFont = new Font("Times new Roman",10);
System.Drawing.RectangleF rectangle = new RectangleF(0,0,36,16);
Random rd = new Random();
int valationNo = 1000 + rd.Next(8999);
g.FillRectangle(new SolidBrush(Color.BurlyWood),rectangle);
g.DrawString(valationNo.ToString(),textFont,new SolidBrush(Color.Blue),rectangle);
newBitmap.Save(Server.MapPath("img")+"\\19.gif",ImageFormat.Gif);
}

[bingbingcha]

private void Page_Load(object sender, System.EventArgs e)
{
if ( !IsPostBack ){

Bitmap newBitmap = new Bitmap(36,16,PixelFormat.Format32bppArgb);
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(newBitmap);
g.FillRectangle(new SolidBrush(Color.White),new Rectangle(0,0,36,16));
System.Drawing.Font textFont = new Font("Times new Roman",10);
System.Drawing.RectangleF rectangle = new RectangleF(0,0,36,16);
Random rd = new Random();
int valationNo = rd.Next(1000,8999);
g.FillRectangle(new SolidBrush(Color.BurlyWood),rectangle);
g.DrawString(valationNo.ToString(),textFont,new SolidBrush(Color.Blue),rectangle);
newBitmap.Save(Server.MapPath("img")+"\\19.gif",ImageFormat.Gif);

g.Dispose();//记得释放资源
newBitmap.Dispose();
}
}

[webwait]

newBitmap.Save(Server.MapPath("img/19.gif"),ImageFormat.Gif);

[Lcindep110]

同意楼上

[rainvoice_zj]

可是还有一个BUG,为什么验证码上的数字始终不变呀.望高手帮我看看哪的错.谢了