Checkchanged event does not fire on uncheck of checkbox in asp.net

i have tested article

Multilevel-N-Level-Nested-GridView-GridView-inside-GridView-in-ASPNet-with-Paging

and added the checkbox in  Orders Gridview as you have added in gvDetails(child) Gridview. Here i am able to see True(checked) and false(Unchecked) in alert box.

Just add the following Html in OrdersGrid:

<asp:TemplateField ItemStyle-Width="20px">
                                    <ItemTemplate>
                                        <asp:CheckBox runat="server" ID="ckbxDetails" AutoPostBack="true" OnCheckedChanged="chkBoxDetails_CheckedChanged"
                                            Checked='<%# Convert.ToBoolean(Eval("ShipRegion") == DBNull.Value ? false : Convert.ToBoolean(Eval("STR_ADMIN_APP"))) %>' />
                                    </ItemTemplate>
                                </asp:TemplateField>

And following event in the cs file:

protected void chkBoxDetails_CheckedChanged(object sender, EventArgs e)
    {
        CheckBox ChkBoxDetails = (CheckBox)sender;
        string message = ChkBoxDetails.Checked.ToString();
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        sb.Append("<script type= 'text/javaScript'>");
        sb.Append("window.onload=function(){");
        sb.Append("alert('");
        sb.Append(message);
        sb.Append("')};");
        sb.Append("</script>");
        ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", sb.ToString());
    }

may be you are having problem with your third party control.

<%@ Register Assembly="Anthem" Namespace="Anthem" TagPrefix="anthem" %>
<%@ Register TagPrefix="pwcontrol" Namespace="PowerWork.PWWebForms" Assembly="PWPForms" %>

use asp:Panel instead of anthem:Panel