I want to close Panel from DynamicServiceMethod of PopUp Control Extender

Question

here is my dyanamic method code -

string sSQLString = "SELECT  * from VIEW_ALLOCATION";
             
            

        dtValue = SQLInterFace.ExecuteDataSet(m_dbase.cnnConnection, sSQLString).Tables[0];

        StringBuilder b = new StringBuilder();

        b.Append("<div id='divPopup' runat='server' style='overflow-y:scroll;overflow-x:hidden;height:150px;'> <table style='background-color:#f3f3f3; border:#336699 3px solid; ");
        b.Append("width:400px; font-size:8px; font-family:Verdana;' cellspacing='0' cellpadding='3'>");
        b.Append("<tr><td colspan='3' style='background-color:#336699; color:white;'>");
        b.Append("<b>C. Heads </b></td> <td align = 'center' style='background-color:#336699; color:white;'>
<input ID='Button1' type='button' value='x' style='border: thin hidden #FFFFFF; background-color: #336699' onclick = 'if(document.getElementById('<%=Panel1.ClientID%>').style.display == 'block')' />");
        b.Append("</td></tr>");
        for (int i = 0; i < dtValue.Rows.Count; i++)
        {
            //b.Append("<tr><td style='width:80px;'><b>Unit Price</b></td>");
            //b.Append("<td style='width:80px;'><b>Stock</b></td>");
            //b.Append("<td><b>Description</b></td></tr>");

            b.Append("<tr>");
            b.Append("<td colspan='4'style='color:Black;' ><b>" + dtValue.Rows[i][Constant.GLHEAD_V].ToString() + "</b></td>");
            b.Append("</tr>");
        }
        b.Append("</table></div>");

        return b.ToString();

here is my html code. I m using grid. Inside the grid i have a image button. When i click on that button pop up appears. I want to close that pop up from Button1 which i m using in dynamic service method.

 <asp:TemplateField HeaderText="Heads">
                                       
                                        <ItemTemplate>
                                            <table cellpadding="0" cellspacing="0" width="100%">
                                                <tr>
                                                    <td valign="top" width="10%">
                                                        <asp:Image ID="imgSubGroup" runat="server" AlternateText="Click for C.Head"
                                                            Height="16" ImageUrl="~/CSS/images/Information.png" ToolTip="Click for C.Head"
                                                            Width="16" />
                                                    </td>
                                                    <td valign="top" width="90%">
                                                        <asp:Label ID="lblSubGroup" runat="server" Font-Names="Tahoma, Arial, Verdana"
                                                            Font-Size="8pt" TEXT='<%# BIND("GLHead_V") %>' />
                                                            
      
       
                                                       <cc1:PopupControlExtender ID="PopupControlExtender1" runat="server"
                                                            DynamicContextKey='<%# Eval("SubGroupCode_N") %>' DynamicControlID="Panel1"
                                                            DynamicServiceMethod="GetDynamicContent" PopupControlID="Panel1"
                                                            Position="Bottom" TargetControlID="imgSubGroup">
                                                        </cc1:PopupControlExtender>
                                                                                                
                                                    </td>
                                                </tr>
                                            </table>
                                        </ItemTemplate>
                                        <HeaderStyle Font-Bold="True" HorizontalAlign="Center" VerticalAlign="Top"
                                            Wrap="False" Width="25%" />
                                        <ItemStyle HorizontalAlign="Left" Width="25%" VerticalAlign="Top" Wrap="False" />
                                    </asp:TemplateField>

-----And my panel is outside the grid--

 <asp:Panel ID="Panel1" runat="server"   CssClass="popupControl">
       
        </asp:Panel>
------i want to close this panel on click of button1--