Background design problem in gridview because of using ajax hoverextender menu

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C#

Hi Friends,

I am using ajax hover extender menu in my gridview. While i am calling javascript alert message my page background displays that hover menu values. How to avoid that.Can anyone help plz...

This is my code

<ItemTemplate>
                                        <asp:ImageButton ID="btnAdd" ValidationGroup="" CausesValidation="true" CommandName=""
                                            runat="server" ImageUrl="~/images/comment.png" CssClass="mar_rgt1" />
                                        &nbsp;
                                        <asp:Image ID="imgFlag" runat="server" ImageUrl='<%#Eval("flag") %>' ToolTip='Special offer' />
                                        </td>
                                        <atk:HoverMenuExtender ID="HoverMenuExtender1" runat="server" PopupControlID="popupImage"
                                            TargetControlID="btnAdd" OffsetX="10" OffsetY="5" PopupPosition="Left" PopDelay="100"
                                            HoverDelay="100">
                                        </atk:HoverMenuExtender>
                                        <asp:Panel runat="server" ID="popupImage" BorderColor="#628BD7" BorderStyle="Solid"
                                            BorderWidth="1px">
                                            <input type="hidden" id="hdncomments" runat="server" value='<%#DataBinder.Eval(Container, "DataItem.Comments")%>' />
                                           
                                            <asp:TextBox runat="server" ID="txt_Comments" TextMode="MultiLine" Height="50px"
                                                disabled="disabled" Width="320px" Text='<%#DataBinder.Eval(Container,"DataItem.Comments") %>'></asp:TextBox>
                                        </asp:Panel>
                                    </ItemTemplate>

Thanks
Guna