Facebook sdk using c#.net (OAuth Exception - #1)

I am developing an app in .net framework using c# which integrate Facebook.

I have following requirements for my app

1. User can login to Facebook account
2. User can view Friends list, Messages & Notifications.

I successfully completed my 1 requirement. There is problem with 2 requirement which I shown below--

 public void Show_Friends()
    {
        try
        {
            fbclient = new FacebookClient("https://graph.facebook.com/endpoint?key=value&access_token=MyappId|MyAppSecret");
            dynamic friendslist = fbclient.Get("/me?fields=friendlists");//Here exception occours
            int numberOfFriends = (int)friendslist.data.Count;
            for(int i = 0; i < numberOfFriends; i++)
            {
                friendsListBox.Items.Add(friendslist.data[i].name);
            }
        }
        catch(Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

Following exception occurs when I call Show_Friends method

(OAuth Exception - #1) Bad Signature