母板页中chechbox全选的问题

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="sendmsg.aspx.cs" Inherits="send_sendmsg" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>无标题页</title>
    <style type="text/css">
        .style1
        {
            width: 80%;
        }
    </style>
</head>    <script language="javascript" type="text/javascript">
function selectAll(ctlName,bool)
{
   var ctl = document.getElementById(ctlName);//根据控件的在客户端所呈现的ID获取控件
   var checkbox = ctl.getElementsByTagName('input');//获取该控件内标签为input的控件
   /*所有Button、TextBox、CheckBox、RadioButton类型的服务器端控件在解释成Html控件后，都为<input type=''..../>，通过type区分它们的类型。*/
   for(var i=0;i<checkbox.length;i++)
   {
       if(checkbox[i].type=='checkbox')
       {
            checkbox[i].checked = bool;
        }
    }
}
    </script>
<body>
    <form id="form1" runat="server">
    <div>
    
        <asp:Image ID="Image1" runat="server" ImageUrl="~/img/3-1.jpg" />
    
    </div>
    <table class="style1">
        <tr>
            <td colspan="5">
                &nbsp;</td>
        </tr>
        <tr>
            <td colspan="5">
                <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
                    DataSourceID="SqlDataSource1">
                    <Columns>
                        <asp:TemplateField HeaderText="选择">
                            <ItemTemplate>
                                <asp:CheckBox ID="CheckBox1" runat="server" />
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:BoundField DataField="phone" HeaderText="phone" SortExpression="phone" />
                        <asp:BoundField DataField="p_time" HeaderText="p_time" 
                            SortExpression="p_time" />
                        <asp:BoundField DataField="message" HeaderText="message" 
                            SortExpression="message" />
                    </Columns>
                </asp:GridView>
                <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
                    ConnectionString="<%$ ConnectionStrings:.netConnectionString %>" 
                    SelectCommand="SELECT [userid], [phone], [p_time], [message] FROM [userinfo]">
                </asp:SqlDataSource>
            </td>
        </tr>
        <tr>
            <td colspan="5">
                <asp:TextBox ID="TextBox1" runat="server" BorderColor="#6699FF" 
                    BorderStyle="Dotted" Columns="55" ForeColor="#6600FF" MaxLength="200" Rows="6" 
                    TextMode="MultiLine"></asp:TextBox>
            </td>
        </tr>
        <tr>
            <td>
                &nbsp;</td>
            <td>
                &nbsp;</td>
            <td>
                &nbsp;</td>
            <td>
               <asp:CheckBox Text="全选/反选" runat="server" ID="cbHead" onclick="javascript:selectAll('GridView1',this.checked);">
                </asp:CheckBox>
            </td>
            <td>
                &nbsp;</td>
        </tr>
        <tr>
            <td>
                &nbsp;</td>
            <td>
                &nbsp;</td>
            <td>
                &nbsp;</td>
            <td>
                <asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False">
                    <Columns>
                        <asp:BoundField DataField="phone" HeaderText="123" SortExpression="phone" />
                    </Columns>
                
                </asp:GridView>
            </td>
            <td>
                &nbsp;</td>
        </tr>
    </table>
    <p>
                <asp:Button ID="Button4" runat="server" Text="Button" 
            onclick="Button4_Click" />
               </p>
    </form>
</body>
</html>
不用母板页可以使用，但是放在母板页里面就无效，求大大解决