jQuery Grid Plugin - jqGrid

I work with ASP .NET, and i shipping this data

{"totalgeneral":"1","paginas":"1","registros":"1","filas":
  [
    {"id":"1", "campos":["1","A253","MonedaHerodes","200","1"]}
  ]
}

my definition for jqgrid is this:

$("#Grilla").jqGrid({
        datatype: "json",
        url: "tratarGrilla.ashx?accion=leerArticulos&empresa=" + empresaActual + "&filasPorPagina=" + nroRenglones + "&totalRegistros=" + totalRegistros + "&losCampos=" + lasColumnas,
        mtype: 'GET',
        height: laAltura,
        rowNum: nroRenglones,
        shrinkToFit: true,
        scrollOffset: 32,
        emptyrecords: "No existen registros para observar",
        loadtext: "Buscando datos.....",
        autowidth: true,
        gridview: true,  // carga mas veloz
        cellLayout: 0,
        loadonce: vLoadOnce,
        onselectrow: true,
        pgbutton: botones,
        pginput: elInput,
        viewrecords: verRegistros,
        loadError: function() { alert('ERROR') },
        loadComplete:
                function(request) {
                    var a = request;
                    alert($(a).val());
                },
        colNames: ['ID', 'Tit2', 'Tit3', 'Tit4', 'Tit5'],
        colModel: [
               { name: 'id', index: 'id', width: 90 },
               { name: 'codigo', index: 'codigo', width: 90 },
               { name: 'descripcion', index: 'descripcion asc', width: 100 },
               { name: 'precio', index: 'precio', width: 80, align: "right" },
               { name: 'cantidad', index: 'cantidad', width: 150, sortable: false}],
        jsonReader: {
            root: "d.filas",
            total: "d.totalgeneral",
            page: "d.paginas",
            records: "d.registros",
            repeatitems: false,
            cell: "campos",
            id: "id"
        },
        caption: laEmpresa.nombreArticulo
    });

When execute, no display data in grid, and in my alert message in event "loadComplete" display null

What is the problem?

Can someone explain with example if JSON WITH ASP .NET AND JQGRID 3.6.5 WORK?

Three days with this problem and i have not a solution.

Tks in advance

From Buenos Aires, Argentina.... Victor