ModularPopUp not poping Up

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C#3.0

C#

I have placed a requiredfieldValidator for a textbox validation and ModularPopUpextender to show up the message.The validation does occurs but only on the server site and no message(popup)occurs at the client site.The Asp code is:

<asp:UpdatePanel ID="update" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
                    <asp:Panel ID="errorsPanel" runat="server" Height="41px"
                        style="margin-left: 54px; margin-top: 144px" Width="812px" BackColor="White">
                        <div style="text-align: left">
                        <asp:ValidationSummary ID="valSummary" runat="server" ShowSummary="true" DisplayMode="BulletList"
        ValidationGroup="valGroup" />

<div style="text-align: right">
       <asp:Button ID="okBtn" runat="server" Text="Ok" /></div>

                        </div>
                    </asp:Panel>
                     <asp:Label ID="invisibleTarget" runat="server" Style="display: none" />
                    <asp:ModalPopupExtender ID="modalPopupEx" runat="server" PopupControlID="errorsPanel"
                      TargetControlID="invisibleTarget" CancelControlID="okBtn" BackgroundCssClass="modalBackground" DropShadow="true">
                    </asp:ModalPopupExtender>
                    </ContentTemplate>
</asp:UpdatePanel>

The method in the master page is:

public partial class SiteMaster : System.Web.UI.MasterPage 
{
    
    public bool CheckErrors()
    {
        //Page x=new System.Web.UI.Page();
        ValidationSummary sum= new ValidationSummary();
        Page.Validate(sum.ValidationGroup);//error is in this line
        if (!Page.IsValid)
        {
           
            //this.EnsureChildControls();
            UpdatePanel update = new UpdatePanel();
            update.ID = "update";
            update.UpdateMode = UpdatePanelUpdateMode.Conditional;
            update.Update();
            modalPopupEx = new AjaxControlToolkit.ModalPopupExtender();
           
            modalPopupEx.Show();
            return false;
        }
        return true;
    }
}

The the click event in the web form is:

protected void ImageButton2_Click(object sender, ImageClickEventArgs e)
    {
        SiteMaster master = (SiteMaster)this.Master;
        if (master.CheckErrors())
        {
            GridView2.Visible = false;
            gvsearch.Visible = true;

            string search = txtsearch.Text.ToString();
            gvsearch.DataSource = DataBase2.myProcedureName(search);
            gvsearch.DataBind();
        }
    }

I have also set the valiadtion group of the controls:(Textbox,RequireFieldValidator and Button)

Thanks