C# webclient cannot getting response from https protocol

When i trying to load html from server by https, it returning an error code 500: but when i open same link in browser it works fine: is there any way to do this? I'm using Webclient and also sending a useragent information to the server:

HttpWebRequest req1 = (HttpWebRequest)WebRequest.Create("m开发者_高级运维obile.unibet.com/";); 
req1.UserAgent = @"Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5";
var response1 = req1.GetResponse();
var responsestream1 = response1.GetResponseStream();

David is correct, this generally happens when the server is expecting some headers that is not passed through, in your case Accept

this code works now

string requestUrl = "https://mobile.unibet.com/unibet_index.t";
var request = (HttpWebRequest)WebRequest.Create(requestUrl);
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
request.UserAgent = "//Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)";

using (var response = request.GetResponse() as HttpWebResponse)
{
 using (var sr = new StreamReader(response.GetResponseStream()))
 {
           var responsestring = sr.ReadToEnd();
       if (!string.IsNullOrEmpty(responsestring))
       {
    Console.WriteLine(responsestring);
           }
  }
 }

This should probably be a comment but there's not enough room in the comment for all the questions... I don't think the question has enough information to answer with any level of confidence.

A 500 error means a problem at the server. The short answer is that the browser is sending some content that the WebClient is not.

The WebClient may not be sending headers that are expected by the server. Does the server require authentication? Is this a page on a company that you've contracted with that perhaps provided you with credentials or an API key that was Do you need to add HTTP Authorization?

If this is something you're doing with a company that you've got a partnership with, you should be able to ask them to help trace why you're getting a 500 error. Otherwise, you may need to provide us with a code sample and more details so we can offer more suggestions.