解析值时遇到意外字符:<路径''，行0，位置0在GA api

在向GA发送请求之前，我使用以下google analytics api代码进行身份验证，但我收到错误消息

"解析值时遇到意外字符:<路径",第0行，GA>

同时执行请求GAOuthService.Data.Ga.Get()方法

我的认证码:

      var scopes = new[] { AnalyticsService.Scope.Analytics, 
                                         AnalyticsService.Scope.AnalyticsEdit, 
                                         AnalyticsService.Scope.AnalyticsManageUsers,   
                                         AnalyticsService.Scope.AnalyticsReadonly};    
        // here is where we Request the user to give us access, or use the Refresh Token that was previously stored in %AppData%
        UserCredential credential = GoogleWebAuthorizationBroker.AuthorizeAsync(new ClientSecrets { ClientId = clientId, ClientSecret = clientSecret }
                                                                                , scopes
                                                                                , userName
                                                                                , CancellationToken.None
                                                                                , new FileDataStore("GoogleAnalytics.Auth.Store")).Result;
        var service = new AnalyticsService(new BaseClientService.Initializer()
                                               {
                                                   HttpClientInitializer = credential,
                                                   ApplicationName = "xyz",
                                               });

var request = service.Data.Ga.Get("ga:8903098", "2014-01-01", "2014-01-01", "ga:sessions");
request.MaxResults = 1000;
GaData result = request.Execute();