Windows 8 HttpClient在SendAsync（C#）上引发错误

我的代码（C#）：

HttpClient实例（HttpClient）总是在标有-->错误注释的行中遇到异常。我找不到任何错误的代码行。异常显示：“基础连接已关闭”，“发送时出错”，但连接未如您所见关闭。我尝试了几个选项，如“UseDefaultCredentials true/false”、“new NetworkCredentials”

我的场景是一个向exchange web服务（ews）发送soap消息的应用程序

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你有什么办法来解决我的问题吗？

小提琴手的轨迹能解释导线上来回的情况吗？这可能是一个比赛条件。如果您使用Send而不是SendAsync，它会工作吗？Fiddler说401未经授权，但正如您在我的代码中看到的那样，我被授权了。没有“Send”，因为我使用的是WinRT。您是否将URL与https://？一起使用？？

        HttpClientHandler httpClientHandler = new HttpClientHandler();
        httpClientHandler.PreAuthenticate = true;
        //httpClientHandler.UseDefaultCredentials = true;
        httpClientHandler.Credentials = CredentialCache.DefaultNetworkCredentials;
        //httpClientHandler.Credentials = new NetworkCredential("usr", "pw", "domain");
        httpClientHandler.CookieContainer = new CookieContainer();

        var httpcontent = new StringContent(content);

        HttpClient httpClient = new HttpClient(httpClientHandler);
        httpClient.DefaultRequestHeaders.ExpectContinue = false;
        httpClient.BaseAddress = ews_url;

        // var request = httpClient.PostAsync(ews_url, httpcontent);
        var requestMessage = new HttpRequestMessage();
        requestMessage.RequestUri = ews_url;
        requestMessage.Content = httpcontent;
        requestMessage.Method = HttpMethod.Post;
        var request = httpClient.SendAsync(requestMessage); 
        HttpResponseMessage response = await request; // --> Error