（在线等）为什么在运行webclient的openRead是出现“远程服务器返回错误 (403)已禁止”

Question

string urlAddress = URL.Substring(0,n);
string filename = URL.Substring(n+1,URL.Length-1-n);
string dir = this.textBox2.Text;
         string path = dir+'\\'+filename; WebRequest wr = WebRequest.Create(urlAddress);
client.DownloadFile(this.textBox1.Text.Trim(),filename);
this.statusBarPanel1.Text="开始接受数据.....";
Stream str = client.OpenRead(urlAddress);
StreamReader sr = new StreamReader(str);
byte[] mbyte = new byte[Convert.ToInt32(str.Length)];
str.Read(mbyte,0,(int)(str.Length));

         FileStream fs = new  FileStream                                   (path,FileMode.OpenOrCreate,FileAccess.Write);
fs.Write(mbyte,0,(int)(str.Length));
str.Close();
fs.Close();