WebClient.UploadValues返回的数据不完整

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System.Net.WebClient wb = new System.Net.WebClient();
System.Collections.Specialized.NameValueCollection header = new System.Collections.Specialized.NameValueCollection();
header.Add("Cookie", "RMID=12644486477806269649965; AF_C=0_http%3A//xxx.com/login/%3Fmode%3Dlogin");
header.Add("Referer", @"http://xxxx.com/login/?mode=login");
wb.Headers.Add(header);
System.Collections.Specialized.NameValueCollection data = new System.Collections.Specialized.NameValueCollection();
data.Add("level", "1");
data.Add("pwd", "5255555");
data.Add("r_url", "");
data.Add("securityIP", "");
data.Add("uid", "512335566");
data.Add("x", "39");
data.Add("y", "33");
byte[] b = wb.UploadValues("http://xxxx.com/login/login.asp", "POST", data);
string strData = System.Text.Encoding.Default.GetString(b);
StreamWriter n = new StreamWriter("c:\\1.htm", false);
n.Write(strData); MessageBox.Show("ok");

返回的页面数据不完整，试了很就不知道为什么，5555555555

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