jquery asp.net ajax asp.net-mvc episerver

Asp.NET action method succeeds but browser receives a 500 with jQuery.ajax

I have a page that makes an AJAX request to update a small pricing section on the page. It works properly when running on my local machine, but when published to our development server, the AJAX call receives a Internal Server Error 500 response. The part that I get lost at is when I attach the debugger and step through the code, the action appears to complete successfully so it seems something happens after the action method runs that causes the 500 but I don't know of any code that runs after the action method.

Here is the .js ajax, the action method, and its response:

_paymentPlanXhr = $.ajax({
            type: "POST",
            url: $("#_Booking_UpdatePaymentUrl").val(),
            data: "purchaseMem="+ purchaseMem +"&sid=" + selectedStudentID,
            cache: false,
            dataType: "json",
            timeout: 120000,
            success: function (response) {
                ...
            },
            error: function (jqXHR, textStatus, errorThrow) {
                _paymentPlanXhr = null;
                $loadingDiv.hide();
                _pendingPaymentPlanUpdate = false;

                //If this was really an error, not the result of our code cancelling the request
                if (textStatus != "abort")
                    $("#divPaymentLoadError").show();
            }
        });

Action Method:

    [HttpPost]
    public ContentResult Booking_UpdatePayment(PsnBookingPage currentPage, bool purchaseMem, Guid sid)
    {
        AjaxResponse result = new AjaxResponse();
        BookingViewModel bookingVM = new BookingViewModel();


        try
        {
            //Code for building the vm omitted for brevity since it succeeds.

            result.Content = this.RenderPartialView(_paymentViewUrl, viewModel, true);
        }
        catch (Exception ex)
        {
            viewModel.AbortView = true;
            viewModel.AbortMessage = "We're sorry! Something went wrong and we were unable to load the view.";
        }

        return result.ToContentResult();
    }

result.ToContentResult:

{"HasError":false,"ErrorMessage":null,"Content":"      <div id=\"divSelectDate\"><div class=\"data-price\">Due Today: $20.00</div><div class=\"data-price\">Due on Event Date: $0.00</div></div>","Data":null}

I don't know if it's a factor, but this is an EPiServer-based site. How can I find the source of the 500?

Edit:

Maybe this is related to EPiServer because even though I have custom errors turned off, the response I get with the 500 has the following instead of the yellow asp.net error screen:

<html>
<head>
    <meta name="robots" content="noindex,nofollow"><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>
        Page could not be loaded
    </title>
    <style type="text/css">
        body{font-size:65%;color:black;background-color:White;}
        form{font-size:1.2em;}
        body,table{font-family:Verdana;font-weight:normal;}
        h1{color: gray;font-size: 1.4em;font-family:Verdana;margin:0.5em 0 0 0;}
        h2{font-size:1.2em;font-weight:bold;}
        h3{display: inline;font-weight:bold;font-size: 1.0em;}
        .ExceptionInfo{margin:0.6em 0 0.6em 0.2em;}
        .StackTrace{font-family:"Lucida Console";}
        th{font-size: 0.8em;text-align:left;white-space: nowrap;}
        td{font-size: 0.7em;}
        .DetailedHeader{font-weight:bold;border: 1px solid black;padding:4px;text-align:center;}
        .ReportForm{font-family:Verdana;font-weight:normal;font-size: 1.0em;color:black;}
        .SubmitButton{font-family:Verdana;font-weight:normal;font-size: 1.0em;color:black;}
    </style>
    <script type="text/javascript">
        <!--
        function onNavigate(newPageLink)
        {
            return -1;
        }

        function onCommand(newCommand)
        {
            return -1;
        }
        // -->
    </script>
</head><body>
    <h1 class="Title">
        Page could not be loaded

    </h1><p style="width:40em;">The link you specified does not work. This may either be the result of temporary maintenance or an incorrect link.
    </p></body></html>

I thought this was a chrome page, but another thread suggests its an EPiServer-generated page.

Solution

You're looking for the globalErrorHandling attribute on the applicationSettings element in episerver section of web.config (or episerver.config).

It could also be on the site element if you're using EPiServer 7 or earlier.