tweet sharp认证don'；t返回访问令牌

tweet sharp身份验证不返回访问令牌当我使用我的帐户访问令牌进行身份验证时（Y）但是当我使用另一个帐户时没有访问令牌返回？这是代码

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private void Button_Click_2(object sender, RoutedEventArgs e)
        {
            GetTwitterToken();
        }

private void GetTwitterToken()
        {
            service = new TwitterService(TwitterSettings.ConsumerKey, TwitterSettings.ConsumerKeySecret);
            var cb = new Action<OAuthRequestToken, TwitterResponse>(CallBackToken);
            service.GetRequestToken("oob", CallBackToken);
        }

void CallBackToken(OAuthRequestToken rt, TwitterResponse response)
        {
            Uri uri = service.GetAuthorizationUri(rt);
            _requestToken = rt;
            this.Dispatcher.Invoke((Action)(() => { BrowserControl.Navigate(uri); }));
        }

private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            if (String.IsNullOrEmpty(pinText.Text))
                MessageBox.Show("Please enter PIN");
            else
            {
                try
                {
                    var cb = new Action<OAuthAccessToken, TwitterResponse>(CallBackVerifiedResponse);
                    service.GetAccessToken(_requestToken, pinText.Text, CallBackVerifiedResponse);
                    BrowserControl.Visibility = Visibility.Collapsed;
                }
                catch
                {
                    MessageBox.Show("", "", MessageBoxButton.OK);
                }
            }
        }
void CallBackVerifiedResponse(OAuthAccessToken at, TwitterResponse response)
        {
            if (at != null)
           {

                Settings1.Default.AccessToken = at.Token;
                Settings1.Default.AccessTokenSecret = at.TokenSecret;
                Settings1.Default.ScreenName = at.ScreenName;
                Settings1.Default.UserId = at.UserId.ToString();
                MessageBox.Show(at.ScreenName);

           }
        }

任何人都可以帮助