javascript – Problems with dynamic Json ASP .Net request

I have a calculation simulator which through events change I made a request to the controller and this returns me a dynamic response, in case the code I had worked and made the request and I requested it correctly, but this consumes a lot of browser or computer memory (I do not know it) and the page became too slow until at one point the requests Ajax they stopped working, so I chose to use Json to do it, use this Example but at one point in the execution I have this error Object reference not set to an instance of an object.

In this way he made my request:

Model:

public class CalculosSolicitud
{
    public decimal ValorSolicitado { get; set; }
    public decimal ValorInteres { get; set; }
    public decimal ValorSeguro { get; set; }
    public decimal ValorEstudio { get; set; }
    public decimal ValorPlataforma { get; set; }
    public decimal ValorIva { get; set; }
    public decimal ValorTotal { get; set; }
}

Controller to Json:

private List ObtenerListaCalculos()
    {
        CalculosSolicitud rta = new CalculosSolicitud();
        liquidar = new Entity.Credito.Common.ResponseCreditoType();
        List Datos = new List()
        {
            new CalculosSolicitud() { ValorSolicitado = rta.ValorSolicitado = liquidar.solicitud.Valor },
            new CalculosSolicitud() { ValorSeguro = rta.ValorSeguro = liquidar.solicitud.ValorSeguro },
            new CalculosSolicitud() { ValorInteres = rta.ValorInteres = liquidar.solicitud.ValorInteres },
            new CalculosSolicitud() { ValorEstudio = rta.ValorEstudio = liquidar.solicitud.CostoEstudio },
            new CalculosSolicitud() { ValorPlataforma =  rta.ValorPlataforma = liquidar.solicitud.CostoPlataforma },
            new CalculosSolicitud() { ValorIva =  rta.ValorIva = liquidar.solicitud.IVA },
            new CalculosSolicitud() { ValorTotal =  rta.ValorTotal = liquidar.solicitud.Total }
        };
        return Datos;
    }

JsonResult:

public JsonResult LlamarJson(int Valor, int Plazo)
    {
        var output = ObtenerListaCalculos();
        return Json(output, JsonRequestBehavior.AllowGet);
    }

In JavaScript:

RangoPlazoCredito.change(function () {
    CreditoPlazo.attr(Value, $(this).val());
    CreditoPlazo1.attr(Value, $(this).val());
    CreditoPlazo2.attr(Value, $(this).val());
    $.ajax({
        type: "POST",
        traditional: true,
        async: false,
        cache: false,
        url: '/Home/LlamarJson',
        context: document.body,
        data: { Valor: RangoValorCredito.val(), Plazo: RangoPlazoCredito.val() },
        success: function (result) {
            alert(result);
            $("#ValorCreditoMostrar").html('');
            $("#ValorCreditoMostrar").append("

" + result.ValorSolicitado + "

"); }, error: function (xhr) { //debugger; console.log(xhr.responseText); console.log("Error has occurred..", xhr); } }); });

In the controller Json When I define the List and its content is when the error generates me Object reference not set to an instance of an object.