HttpClient - 在vCloud Director上发送get请求时出错

Question

自从昨晚以来，我一直在为这个问题敲打头脑。它仅发生在Windows Server 2012 IIS中已部署的二进制文件中，没有明确的错误日志。但在Visual Studio中，完全没问题。

try
{
    using (var client = new HttpClient())
    {
        var requestUri = "http://[some-vcloud-ipaddress]/api/versions";

        var response = await client.GetAsync(requestUri);           // <-- This is line 94

        if (response.IsSuccessStatusCode)
        {
            var xml = await response.Content.ReadAsStreamAsync();
            var result = Serializer<SupportedVersions>.Deserialize(xml);
            return result;
        }
        return null;
    }
}
catch (Exception ex)
{
    _logger.ErrorFormat("VcloudApiClient - GetSupportedVersions failed. Error message: {0}", ex.Message);

    _logger.ErrorFormat("VcloudApiClient - GetSupportedVersions failed. Error stacktrace: {0}", ex.StackTrace);

    throw;
}

以下是错误日志。

VcloudApiClient - GetSupportedVersions failed. Error message: An error occurred while sending the request.

VcloudApiClient - GetSupportedVersions failed. Error stacktrace:    at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at SomeProject.Tpl.VcloudDirector.VcloudApiClient.<GetSupportedVersions>d__1.MoveNext() in d:\Projects\SomeProject-01\src\Api\SomeProject.Tpl\VcloudDirector\VcloudApiClient.cs:line 94

请注意，在任何其他客户端（浏览器，Postman REST客户端等）上执行URL都没有问题。