GetResponse() 抛出异常 500错误

public static CookieContainer GetCooKie(string loginUrl, string postdata, HttpHeader header)
        {         
            HttpWebRequest request = null;   
            HttpWebResponse response = null;  
            try   
            {      
                CookieContainer cc = new CookieContainer();   
                request = (HttpWebRequest)WebRequest.Create(loginUrl);  
                request.Method = header.method; 
                request.ContentType = header.contentType; 
                byte[] postdatabyte = Encoding.UTF8.GetBytes(postdata);  
                request.ContentLength = postdatabyte.Length;  
                request.AllowAutoRedirect = true;          
                request.CookieContainer = cc;
                request.KeepAlive = true;
                //request.v
                
                //            myHttpWebRequest.Referer = "http://order.xiaomi.com/site/login";
                //提交请求          
                Stream stream;    
                stream = request.GetRequestStream();  
                stream.Write(postdatabyte, 0, postdatabyte.Length);  
                stream.Close();        
                //接收响应          
                response = (HttpWebResponse)request.GetResponse(); 
                response.Cookies = request.CookieContainer.GetCookies(request.RequestUri); 
                CookieCollection cook = response.Cookies; 
                //Cookie字符串格式              
                string strcrook = request.CookieContainer.GetCookieHeader(request.RequestUri); 
                return cc;     
            }          
            catch (Exception ex)  
            {                 
                throw ex;     
            }   
        }      以上是代码，测试人人网通过了 但是过了一个网站就不行了 就总是出错