javaScript Not Working With UpdatePanel ASP.NET

Hi everyone

I'm new in asp.net, I have a problem in using javaScript with update panel, I will appreciate if any body help

I have a textbox and listbox, the textbox filter listbox values using following javascript codes:

<script type="text/javascript">

        var ddlText2, ddlValue2, ddl, ddl2, lblMesg;

        function CacheItems() {
            ddlText2 = new Array();
            ddlValue2 = new Array();
            ddl2 = document.getElementById("<%=lstbCourses.ClientID %>");

            for (var i = 0; i < ddl2.options.length; i++) {
                ddlText2[ddlText2.length] = ddl2.options[i].text;
                ddlValue2[ddlValue2.length] = ddl2.options[i].value;
            }
        }

        window.onload = CacheItems;

        function FilterItems2(value) {
            document.getElementById('<%=lstbCourses.ClientID%>').selectedIndex = -1;
            ddl2.options.length = 0;
            for (var i = 0; i < ddlText2.length; i++) {
                if (ddlText2[i].toLowerCase().indexOf(value) != -1) {
                    AddItem2(ddlText2[i], ddlValue2[i]);
                }
            }
            lblMesg.innerHTML = ddl2.options.length + " items found.";
            if (ddl2.options.length == 0) {
                AddItem2("No items found.", "");
            }
        }

        function AddItem2(text, value) {
            var opt = document.createElement("option");
            opt.text = text;
            opt.value = value;
            ddl2.options.add(opt);
        }</script>

and here is the textbox and the list box.

<asp:TextBox ID="TextBox1" runat="server" onkeyup="FilterItems2(this.value)" Width="148px"></asp:TextBox><br /><br /><asp:ListBox ID="lstbCourses" runat="server" Height="172px" Width="200px" AutoPostBack="True"
                                DataSourceID="sqdsFields" DataTextField="FieldName" DataValueField="FieldSerial"></asp:ListBox>

They work fine in normal page, but when i embed the listbox and the textbox inside update panel, only run first time, after selecting a value from listbox they will not work.

following code with updatepanel not working

<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:TextBox ID="TextBox1" runat="server" onkeyup="FilterItems2(this.value)" Width="148px"></asp:TextBox><br /><br /><asp:ListBox ID="lstbCourses" runat="server" Height="172px" Width="200px" AutoPostBack="True"
                DataSourceID="sqdsFields" DataTextField="FieldName" DataValueField="FieldSerial"></asp:ListBox><asp:SqlDataSource ID="sqdsFields" runat="server" ConnectionString="<%$ ConnectionStrings:amarefarsdbConnectionString %>"
                SelectCommand="SELECT FieldSerial, FieldName FROM eduFieldOfStudy ORDER BY FieldName"></asp:SqlDataSource></ContentTemplate></asp:UpdatePanel><asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"
        DisplayAfter="50"><ProgressTemplate><div><asp:Image ID="imgProgress" ImageUrl="~/Icons/ajax-loader.gif" runat="server" /></div></ProgressTemplate></asp:UpdateProgress>

I see in internet problem is due to postback of update panel, but could not resolve.

Plase help

thank you

regards hiraz