Facing issue while trying to Comment on a Post Facebook in MVC3

Question

I am trying to send the reply to a Facebook Post.

Below is my action method

public ActionResult GetMyDetails()
{
    var fb = new Facebook.FacebookClient("appId", "appSecret");
    dynamic obj = fb.Post(
                          "https://facebook.com/
                           PostID/
                           comments/?message=ws&access_token=" + fb.AccessToken
                         );
}

Query - I basically want to know, why A comment on Post using the above code is not working ?