Ajax Post在IIS托管网站中提供内部服务器错误500

Question

$.ajax({
            url: "/Home/ReadText",
            type: "POST",
            cache: false,
            async: false,
            data: function () {
               var data = new FormData();
                data.append("file", jQuery("#file").get(0).files[0]);
               data.append("selected", drop);
               return data;
            }(),
            contentType: false,
            processData: false,
            success: function (response) {
               debugger;
                $("#target").empty();
               $("#target").load("/Home/Results");


            },
            error: function (jqXHR, textStatus, errorMessage) {
                console.log(errorMessage);
            }
        });

  

异常详细信息：System.NullReferenceException：未将对象引用设置为对象的实例。

   [HttpPost]
    public ActionResult ReadText(HttpPostedFileBase file, string selected)
       {
     if (file != null && file.ContentLength > 0)
                {
                    var fileName = Path.GetFileName(file.FileName);
                    Session["filename"] = fileName.Replace(".txt","");
                    string content = file.InputStream.ToString();
                    path = Path.Combine(Server.MapPath("~/UploadedImages/"), fileName);
                    file.SaveAs(path);
                    }
                string texts = System.IO.File.ReadAllText(path);
                texts = texts.Replace(","," ");
                    string ofile = "names.txt";
                    string Spellpath= Path.Combine(Server.MapPath("~/MegTrans/"), ofile);
                    TextWriter tw1 = new StreamWriter(Spellpath, false, Encoding.Default);


                    tw1.WriteLine(texts);

                    tw1.Close();
Session["score"] = texts;
            return PartialView("Results");
       }

这里返回一个局部视图，并在ajax调用的成功函数中重新加载视图。它在本地运行时正常工作，ReadText（）方法在IIS托管网站上进行ajax调用时给出内部服务器错误

我从Chrome中的开发模式获得了异常的堆栈跟踪。

[NullReferenceException: Object reference not set to an instance of an object.]
   Tesseract_MVC_Test.Controllers.HomeController.ReadText(HttpPostedFileBase file, String selected) +1675
   lambda_method(Closure , ControllerBase , Object[] ) +190
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +228
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +34
   System.Web.Mvc.Async.AsyncControllerActionInvoker.<BeginInvokeSynchronousActionMethod>b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState) +38
   System.Web.Mvc.Async.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult) +70
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +68
   System.Web.Mvc.Async.AsyncInvocationWithFilters.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3d() +71
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +386
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +69
   System.Web.Mvc.Async.<>c__DisplayClass2b.<BeginInvokeAction>b__1c() +38
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +186
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +59
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +29
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +53
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +36
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +38
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +44
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +399
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +157