为什么我的JSON结果方法返回响应错误（500）？

这个问题已经有了答案:

从客户端检测到潜在危险的请求表单值

我在我的ASP.net MVC应用程序中执行AJAX文件上传操作，其中我还使用angularjs。

服务方法调用：

    uploadFile: function() {
        var defer = $q.defer();
        var fileInput = document.getElementById("files");
        var messageHeaders = { 'Content-Type': 'application/x-www-form-urlencoded' };
        messageHeaders['X-File-Name'] = encodeURI(fileInput.files[0].name);
        messageHeaders['X-File-Type'] = encodeURI(fileInput.files[0].type);
        var fileData = fileInput.files[0];
        $http({
            url: window.ROOT + 'EmployerBenefit/UploadFile',
            method: "POST",
            data: fileData,
            headers: messageHeaders
        }).success(function(callback) {
            defer.resolve(callback);
        });
        return defer.promise;
    },

控制器方法：

[AllowAnonymous]
public JsonResult UploadFile(string attachmentType, int planId = 24527)
{
    var success = true;
    string message = ApplicationMessage.InvalidParameter;
    // Validation part removed
    if (success)
    {
        var inputStream = Request.InputStream;
        var fileLenght = (int) inputStream.Length;
        var fileName = HttpUtility.UrlDecode(Request.Headers["X-File-Name"]);
        var bytes = new byte[fileLenght];
        Request.InputStream.Read(bytes, 0, fileLenght);
        if (!Directory.Exists(Server.MapPath("/Content/Images/" + CommonFunctions.ParseString(planId))))
        {
            Directory.CreateDirectory(Server.MapPath("/Content/Images/" + CommonFunctions.ParseString(planId)));
        }
        System.IO.File.WriteAllBytes(
            Server.MapPath("/Content/Images/" + CommonFunctions.ParseString(planId) + "/" + fileName), bytes);
    }
    Response.StatusCode = (int)HttpStatusCode.OK;
    return Json(new {success, message}, JsonRequestBehavior.AllowGet);
}

问题：

我在工厂中设置了一个拦截器来处理响应错误，即使我将响应状态设置为OK，拦截器也会捕获响应错误（500）

我错在哪里了？