通过WebClient对JSON返回URL的请求抛出异常

我通过使用WebClient发送一个请求到Facebook Graph API，下面的代码是在ASP.net MVC控制器类中编写的:

 WebClient client2 = new WebClient();
        Stream data2 = client2.OpenRead("https://graph.facebook.com/me&" + s);
        StreamReader reader2 = new StreamReader(data); //Error

        string s2 = reader2.ReadToEnd();
        data2.Close();
        reader2.Close();
        s2=s2.Substring(s2.IndexOf('"', s2.IndexOf(':')), s2.Length - s2.IndexOf('"', s2.IndexOf(':')));
        s2= s2.Substring(1, s2.IndexOf('"', 1) - 1);
        return "AccessToken Stored in session, Current Signed in user is: "+s2;

我得到这个错误:"System. "ArgumentException: Stream was not readable."在注释为//错误的行。对https://graph.facebook.com的请求以JSON格式返回数据。这是导致这个异常的原因吗?请帮助。如何解决这个问题?