I have 2 comboboxes. On selected index change of one combobox I want to bind the next combobox. Please check the code below and let me know where am i going wrong.

<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>

<script runat="server">
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!X.IsAjaxRequest)
        {

            Store store = this.ComboBox1.GetStore();
            store.DataSource = new object[] 
            { 
                new object[] { "1", "--Select Maturity--", "black","white" },
                new object[] { "2", "Gaps", "white","red" },
                new object[] { "3", "Disconnects", "white","pink" },
                new object[] { "4", "Actions", "black","yellow" },
                new object[] { "5", "In Place", "black","lightgreen" },
                new object[] { "6", "Proven", "white","green" },
                new object[] { "7", "N/A", "black","lightgray" }
            };


        }
    }
</script>


<style type="text/css">
    .x-form-text {
        background: none !important;
        background-image: none !important;
        /*color: white !important;*/
        font-weight: bold !important;
        text-align: center !important;
    }
</style>

<ext:XScript ID="XScriptdd1" runat="server">
    <script type="text/javascript">
        var applyFilter = function (field) {

            var MaturityHealth = field.value;
            if (MaturityHealth == '1') {//-->Gaps - Red.
                field.el.dom.style.color = "white !important";
                field.el.dom.style.textAlign = "center";
                field.el.dom.style.backgroundColor = "#FF0000";
                field.el.dom.style.backgroundImage = "none";
            }
            else if (MaturityHealth == '2') {//-->Disconnect - LightRed.
                field.el.dom.style.color = "white";
                field.el.set().dom.style.background = "#FF8080";
                field.el.dom.style.backgroundColor = "#FF8080";
                //field.el.dom.style.backgroundImage = "none";
            }
            else if (MaturityHealth == '3') {//-->Actions - Yellow
                field.el.dom.style.color = "black";
                field.el.set().dom.style.backgroundColor = "black"; //field.el.dom.style.backgroundColor = "#FFFF00";
                field.el.dom.style.backgroundImage = "none";
            }
            else if (MaturityHealth == '4') {//-->In Place - LightGreen
                field.el.dom.style.color = "black";
                field.el.dom.style.backgroundColor = "#C2FFA3";
                field.el.dom.style.backgroundImage = "none";
            }
            else if (MaturityHealth == '5') {//-->Proven - Green
                field.el.dom.style.color = "white";
                field.el.dom.style.backgroundColor = "#008000";
                field.el.dom.style.backgroundImage = "none";
            }
            else if (MaturityHealth == '6') {//-->N/A - Grey
                field.el.dom.style.color = "black";
                field.el.dom.style.backgroundColor = "#d4d0c8";
                field.el.dom.style.backgroundImage = "none";
            }
            else {
                field.el.dom.style.color = "white";
                field.el.dom.style.backgroundColor = "white";
                field.el.dom.style.backgroundImage = "none";
            }
            field.el.dom.style.fontWeight = "bold";
        };
        </script>
</ext:XScript>
<!DOCTYPE html>

<html>
<head id="Head1" runat="server">
    <title>Ext.NET v2 Example</title>
</head>
<body>
    <form id="Form1" runat="server">
        <ext:ResourceManager ID="ResourceManager1" runat="server" Namespace="" />
        <ext:Store ID="Store3" runat="server">
            <Model>
                <ext:Model ID="Model3" runat="server">
                    <Fields>
                        <ext:ModelField Name="value" />
                        <ext:ModelField Name="text" />
                        <ext:ModelField Name="color" />
                        <ext:ModelField Name="bgcolor" />
                    </Fields>
                </ext:Model>
            </Model>
        </ext:Store>

        <ext:Store ID="Store4" runat="server">
            <Model>
                <ext:Model ID="Model4" runat="server">
                    <Fields>
                        <ext:ModelField Name="value" />
                        <ext:ModelField Name="text" />
                        <ext:ModelField Name="color" />
                        <ext:ModelField Name="bgcolor" />
                    </Fields>
                </ext:Model>
            </Model>

        </ext:Store>
        <ext:ComboBox
            ID="ComboBox1"
            runat="server"
            DisplayField="text"
            ValueField="value">
            <Store>
                <ext:Store ID="Store1" runat="server">
                    <Model>
                        <ext:Model ID="Model1" runat="server">
                            <Fields>
                                <ext:ModelField Name="value" />
                                <ext:ModelField Name="text" />
                                <ext:ModelField Name="color" />
                                <ext:ModelField Name="bgcolor" />
                            </Fields>
                        </ext:Model>
                    </Model>
                    <Reader>
                        <ext:ArrayReader />
                    </Reader>
                </ext:Store>
            </Store>
            <Listeners>
                <Select Handler="applyFilter(this)" />
                <AfterRender Handler="applyFilter(this)" />
            </Listeners>
            <ListConfig>
                <Tpl ID="Tpl1" runat="server">
                    <Html>
                        <ul class="x-list-plain">
                            <tpl for=".">
                                <li role="option" class="x-boundlist-item" style="font-weight:bold; text-align:center; background-color:{bgcolor}; color:{color}">
                                    {text}
                                </li>
                            </tpl>
                        </ul>
                    </Html>
                </Tpl>
            </ListConfig>
            <DirectEvents>
                <Select OnEvent="ddlTier3_SelectedIndexChanged">
                </Select>
            </DirectEvents>
        </ext:ComboBox>


        <ext:ComboBox
            ID="ComboBox4"
            runat="server"
            DisplayField="text"
            ValueField="value" Selectable="true" StoreID="Store4">

            <Listeners>
                <Select Handler="applyFilter(this)" />
                <AfterRender Handler="applyFilter(this)" />
            </Listeners>
            <ListConfig>
                <Tpl ID="Tpl3" runat="server">
                    <Html>
                        <ul class="x-list-plain">
                            <tpl for=".">
                                <li role="option" class="x-boundlist-item" style="font-weight:bold; text-align:center; background-color:{bgcolor}; color:{color}">
                                    {text}
                                </li>
                            </tpl>
                        </ul>
                    </Html>
                </Tpl>
            </ListConfig>
        </ext:ComboBox>
    </form>
</body>
</html>

On selected index changed of the first combo :

       protected void ddlTier3_SelectedIndexChanged(object sender, DirectEventArgs e)
        {
            try
            {
                Store strNew = ComboBox4.GetStore();

                strNew.DataSource = new object[] 
                { 
                    new object[] { "1", "--Select Maturity--", "black","white" },
                    new object[] { "2", "Gaps", "white","red" },
                    new object[] { "3", "Disconnects", "white","pink" },
                    new object[] { "4", "Actions", "black","yellow" },
                    new object[] { "5", "In Place", "black","lightgreen" },
                    new object[] { "6", "Proven", "white","green" },
                    new object[] { "7", "N/A", "black","lightgray" }
                };
                strNew.DataBind();
            }
            catch
            {
                throw;
            }
        }