求助！c# 获取网页源码失败，返回错误442

protected string getHtml(string url)

{

string html = "";

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

request.Accept = "*/*";

HttpWebResponse response = null;

Stream stream = null;

StreamReader reader = null;

try

{

response = (HttpWebResponse)request.GetResponse();

stream = response.GetResponseStream();

reader = new StreamReader(stream, Encoding.Default);

html = reader.ReadToEnd();//.Replace("\r\n", ""); 

}

catch (Exception excpt)

{

MessageBox.Show(excpt.Message);

}

finally

{

if (reader != null)

{

reader.Close();

reader.Dispose();

}

if (stream != null)

{

stream.Close();

stream.Dispose();

}

if (response != null)

{

response.Close();

}

}

return html;

}