Child gridview losing focus on button click

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ASP.NET

Gridview

I have done a scenario as follows, I am having a grid view which is having another grid view as Item template of that grid view. Initially I binded a radio button and the required fields from the database. When ever user selects a radio button I will show the corresponding details in another gridi vew. This grid view has some necessary fields with check boxes. When I select a check box and click on a button out side the grid view I am unable to execute the required that was written

<asp:Panel CssClass="grid" ID="pnlCust" runat="server">
        <asp:GridView ID="gvCustomers" AutoGenerateColumns="False" DataKeyNames="EmpID" runat="server"
            ShowHeader="true" BackColor="White" BorderColor="#DEDFDE" BorderStyle="None"
            BorderWidth="1px" CellPadding="4" ForeColor="Black" GridLines="Vertical">
            <AlternatingRowStyle BackColor="White" />
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <%--<asp:Image ID="imgCollapsible" CssClass="first" ImageUrl="~/Assets/img/plus.png"
                                        Style="margin-right: 5px;" runat="server" /><span class="header">
                                            <%#Eval("EmpID")%>
                                            :
                                            <%#Eval("empname")%>--%>
                        <asp:RadioButton ID="rdbtn" runat="server" onclick="RadioCheck(this);" OnCheckedChanged="radio_changed"
                            Text='<%# Bind("EmpID") %>' AutoPostBack="true"></asp:RadioButton>
                        <asp:GridView AutoGenerateColumns="false" CssClass="grid" ID="gvOrders" runat="server"
                            PageSize="1" ShowHeader="true" EnableViewState="false" DataKeyNames="EmpID" OnPageIndexChanging="gvOrders_PageIndexChanging">
                            <RowStyle CssClass="row" />
                            <AlternatingRowStyle CssClass="altrow" />
                            <Columns>
                                <asp:BoundField HeaderText="Employee Id" DataField="EmpID">
                                    <ItemStyle HorizontalAlign="Center" Width="100px" />
                                </asp:BoundField>
                                <asp:TemplateField ItemStyle-CssClass="rownum">
                                    <ItemTemplate>
                                        <%# Container.DataItemIndex + 1 %>
                                    </ItemTemplate>
                                </asp:TemplateField>
                                <asp:TemplateField HeaderStyle-BackColor="#EFF1F1" ItemStyle-HorizontalAlign="Center"
                                    ItemStyle-Height="25" HeaderStyle-Width="50" ItemStyle-Width="50">
                                    <HeaderTemplate>
                                        <input id="chkBoxAll" type="checkbox" onclick="checkAllBoxes()" />
                                    </HeaderTemplate>
                                    <ItemTemplate>
                                        <asp:CheckBox ID="chkBoxChild" runat="server" />
                                    </ItemTemplate>
                                </asp:TemplateField>
                                <asp:BoundField DataField="PayPeriodNumber" HeaderText="PayPeriod" HeaderStyle-BackColor="#EFF1F1"
                                    ItemStyle-HorizontalAlign="Center" HeaderStyle-Width="80" ItemStyle-Width="80">
                                </asp:BoundField>
                                <asp:BoundField DataField="PayRollYear" HeaderText="Payroll Year" HeaderStyle-BackColor="#EFF1F1"
                                    ItemStyle-HorizontalAlign="Center" HeaderStyle-Width="100" ItemStyle-Width="100">
                                </asp:BoundField>
                                <asp:BoundField DataField="PaymentDate" HeaderText="Payment Date" HeaderStyle-BackColor="#EFF1F1"
                                    ItemStyle-HorizontalAlign="Center" HeaderStyle-Width="110" ItemStyle-Width="110">
                                </asp:BoundField>
                            </Columns>
                        </asp:GridView>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
            <FooterStyle BackColor="#CCCC99" />
            <HeaderStyle BackColor="#6B696B" Font-Bold="True" ForeColor="White" />
            <PagerStyle BackColor="#F7F7DE" ForeColor="Black" HorizontalAlign="Right" />
            <RowStyle BackColor="#F7F7DE" />
            <SelectedRowStyle BackColor="#CE5D5A" Font-Bold="True" ForeColor="White" />
            <SortedAscendingCellStyle BackColor="#FBFBF2" />
            <SortedAscendingHeaderStyle BackColor="#848384" />
            <SortedDescendingCellStyle BackColor="#EAEAD3" />
            <SortedDescendingHeaderStyle BackColor="#575357" />
        </asp:GridView>
    </asp:Panel>
    <asp:Button ID="btn" runat="server" Text="Delete" onclick="btn_Click" />

Sample Images

http://i.stack.imgur.com/ZM96f.jpg

http://i.stack.imgur.com/ULWTM.jpg

Code for delete button

protected void btn_Click(object sender, EventArgs e)
    {
        foreach (GridViewRow gvRow1 in gvCustomers.Rows)
        {
            GridView gv = (GridView)gvRow1.FindControl("gvOrders");
            foreach (GridViewRow gvrow in gv.Rows)
            {
                CheckBox chkBoxChild = (CheckBox)gvrow.FindControl("chkBoxChild");
                if (chkBoxChild.Checked)
                {

                }
            }
        }
    }

Unable to execute my condition when I select a check box and running the code. Any help please. Also how can I work out Select All check box scenario in the child grid view.