Problem with combobox

Hello, I need help with the following error:
Uncaught TypeError: Cannot read property ‘getElementsByTagName’ of null
I have completely revised and not what is the error.

my code

$(document).ready(function() {
         window.dhx_globalImgPath ="<?php echo base_url() ?>"+"imagenes/";
        d = new dhtmlXCombo("comboAlmacen", "alfa2", 200);
        d.load("<?php echo base_url() ?>autocomplete/almacen_ajax",default_vals);
        d.enableFilteringMode(true);
        e = new dhtmlXCombo("comboResponsable", "alfa2", 200);
        e.load("<?php echo base_url() ?>autocomplete/responsable_ajax",default_vals);
        e.enableFilteringMode(true);
        f = new dhtmlXCombo("comboTipoEntrada", "alfa2", 200);
        f.load("<?php echo base_url() ?>autocomplete/tipoEntrada_ajax",default_vals);
        f.enableFilteringMode(true);
        g = new dhtmlXCombo("comboProveedor", "alfa2", 200);
        g.load("<?php echo base_url() ?>autocomplete/proveedores_ajax",default_vals);
        g.enableFilteringMode(true);      
        r = new dhtmlXCombo("comboRepuesto", "alfa2", 100);
        r.load("<?php echo base_url() ?>autocomplete/repuesto_ajax");
        rd = new dhtmlXCombo("comboRepuestoDes", "alfa2", 220);
        rd.load("<?php echo base_url() ?>autocomplete/repuestoDes_ajax");
        r.enableFilteringMode(true);

       rd.enableFilteringMode(true);

        r.attachEvent("onBlur",asignaDes);

        rd.attachEvent("onBlur",asignaRp);

    });

my html

echo '<td>' . form_label("Proveedor:") . '</td>';
echo '<td>';
echo '<div id="comboProveedor" style="width:200px; height:30px"></div>';
echo '</td>';
echo '</td>';
echo '</tr>';
echo '<tr>';
echo '<td>' . form_label("Almacen:") . '</td>';
echo '<td>';
echo '<div id="comboAlmacen" style="width:200px; height:30px"></div>';
echo '</td>';
echo '<td>' . form_label("Responsable:") . '</td>';
echo '<td>';
echo '<div id="comboResponsable" style="width:200px; height:30px"></div>';
echo '</td>';
echo '<td>' . form_label("Tipo Documento:") . '</td>';
echo '<td>';
echo '<div id="comboTipoEntrada" style="width:200px; height:30px"></div>';
echo '</td>';
echo '</tr>'

if anyone can help me. or need some other data. thank you very much to all and I apologize for my bad English

JAAB

Hello
Provide us please a direct link to your project on support@dhtmlx.com with a link to this topic