Modal popup textbox textchange not working

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>            
                <ajaxToolkit:ToolkitScriptManager ID ="ToolkitScriptManager1" runat ="server"></ajaxToolkit:ToolkitScriptManager>
                <asp:HiddenField ID = "HiddenField1" runat="server" />                          
            <ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" PopupControlID="divPopUpBranch"
                        TargetControlID="hidden"
                        PopupDragHandleControlID="panelDragHandleDiv"
                        BackgroundCssClass="ModalStyle">
            </ajaxToolkit:ModalPopupExtender>
            <div id="div1" style="display: none;">
                <asp:Panel runat="Server" ID="panel1" CssClass="drag">
                    <div class="gridContainer">
                        <asp:PlaceHolder ID="LoadUserContrl" runat="server"></asp:PlaceHolder>    
                    </div>
                    <div class="closeContainer">
                        <div class="closeButton">
                            <asp:Button ID="Button1" runat="server" Text="Close" />
                        </div>
                    </div>
                </asp:Panel>
            </div>        
        </ContentTemplate>        
    </asp:UpdatePanel>

<asp:UpdatePanel ID="UpdateBcode" runat="server" UpdateMode="Conditional">    
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="txtSearchBCode" EventName="TextChanged" />
                    </Triggers>
                    <ContentTemplate>                            
                        <asp:TextBox ID="txtSearchBCode" CssClass="WriteBackColor" runat="server" Style="text-transform: uppercase;
                                width: 60px;" Width="89px" EnableViewState="true" AutoPostBack="true" 
                                MaxLength="3"></asp:TextBox>                   
                    </ContentTemplate>
                </asp:UpdatePanel>

Protected Sub txtSearchBName_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtSearchBName.TextChanged
       Dim Input As String = Server.HtmlEncode(Trim(Me.txtSearchBName.Text))
       If Page.IsPostBack Then
           Me.gvBranch.DataSource = SearchBy("name", Input)
           Me.gvBranch.DataBind()
       End If
   End Sub