Why is this ajax call failing?

Why is this ajax call failing?

I'm hitting the "error" part of this ajax call, seeing "'error in btnTestProduceUsageSettings'":

  1. $("#btnTestProduceUsageSettings").click(function () {
                var dom = $('#dayofmonthselect').val();
                var ord = $('#ordinalselect').val();
                var dow = $('#dayofweekselect').val();
                var wom = $('#weekormonthselect').val();
                var daterangefromval = $('#produsagefrom').val(); 
                var daterangetoval = $('#produsageto').val();
                var unitval = $('#unitsselect').val();
                var reportId = 1;

                $.ajax({
                    type: 'GET',
                    url: '@Url.Action("GetTestSettingVals", "TestSettings")',
                    data: { unit: unitval, report: reportId, dayofmonth: dom, ordinal: ord, dayofweek: dow, 
    weekormonth: wom, fromval: daterangefromval, toval: daterangetoval },
                    cache: false,
                    success: function (returneddata) {
                        var nextgendate = returneddata.testsettings.NextGenDate;
                        var nextfromdate = returneddata.testsettings.NextFromDate;
                        var nexttodate = returneddata.testsettings.NextToDate;

                        alert('If you save the current configuration, the Produce Usage report would next be 
    sent on ' + nextgendate + ' and cover data from ' + nextfromdate + ' to ' + nexttodate);
                    },
                    error: function () {
                        alert('error in btnTestProduceUsageSettings');
                    }
                });

            }); 

JSLint doesn't find anything really wrong with it (beyond its usual nitpickiness). At least one of 

the params is always null. I wondered it that was the problem, but I tried this, just to make sure the null values were not causing the problem:

  1. . . .
    var ord = ''; //$('#ordinalselect').val();
    var dow = ''; //$('#dayofweekselect').val();
    var wom = ''; //$('#weekormonthselect').val();
  2. . . .

...and it still failed.

The Controller method that is supposed to be called isn't being reached at all because of the failure. It is defined:

  1. public JsonResult GetTestSettingVals(string unit, int RptID, string dayOfMonthGen, 
  2.                         string ordinalGen, string dayOfWeekGen, string weekOrMonthGen, 
  3.                         int fromIntDateRange, int  toIntDateRange)

So stepping through the code, with a breakpoint in Chrom Dev Tools, I reach the "$.ajax({" line, but not the breakpoint in the Controller method (in Visual Studio), which has one on the last line shown below:

  1.     public class TestSettingsController : Controller
        {
            public JsonResult GetTestSettingVals(string unit, int RptID, string dayOfMonthGen, string ordinalGen, string dayOfWeekGen, string weekOrMonthGen, int fromIntDateRange, int toIntDateRange)
            {
                TestSettingsModel model = new TestSettingsModel();

I have other ajax/controller combinations designed the same way that work fine, so I can't see what the hangup is here...am I missing an either obvious or well-concealed problem here?