验证CheckBoxList至少要有一项选中（转载）

<script language="javascript" type="text/javascript"> 
        <!--
        function  ClientValidate(sender, args)
        {
            var flag = false;
            var  inarr=form1.all.tags("input");
            for (var i=0; i<inarr.length; i++)
            {
                if(inarr[i].type=="checkbox")
                 {
                    if(inarr[i].checked==true)    
                     {
                         flag = true;
                     }
                  }
             }
             if (flag)
             {
                args.IsValid = true;
             }
             else
             {
                args.IsValid = false;
             }
        }
        -->
</script>
<tr>
    <td align="right" bgcolor="#FFFFFF">用户权限：&nbsp;</td>
    <td bgcolor="#FFFFFF"><asp:CheckBoxList ID="cblrighgs" runat="server" RepeatLayout="Flow" RepeatColumns="5">
        </asp:CheckBoxList>
        <asp:CustomValidator ID="CustomValidator1" runat="server" ClientValidationFunction="ClientValidate"
            Display="Dynamic" ErrorMessage="请选择用户权限"></asp:CustomValidator></td>
  </tr>

这种方法在masterpage中不起作用，不知道怎么解决。