Download file in asp.net from gridview

 .aspx code
<asp:GridView ID="Grid_Circular_meeting" runat="server" AutoGenerateColumns="False"
                                CellPadding="4" Width="95%" EmptyDataText="No Record Exists!!!" AllowPaging="false"
                                ForeColor="#333333" GridLines="None" DataKeyNames="AutoId" OnRowCommand="Grid_Circular_meeting_RowCommand"
                                OnRowDeleting="Grid_Circular_meeting_RowDeleting" OnSelectedIndexChanged="Grid_Circular_meeting_SelectedIndexChanged">
                                <Columns>
                                    <asp:BoundField HeaderText="Title" DataField="Title" HeaderStyle-HorizontalAlign="Left">
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:BoundField>
                                    <asp:BoundField HeaderText="MeetingDate" DataField="MeetingDate" DataFormatString="{0:dd-MMM-yyyy}"
                                        HeaderStyle-HorizontalAlign="Left">
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:BoundField>
                                    <asp:BoundField HeaderText="Location" DataField="Location" DataFormatString="{0:dd-MMM-yyyy}"
                                        HeaderStyle-HorizontalAlign="Left">
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:BoundField>
                                    <asp:BoundField HeaderText="MeetingTime" DataField="MeetingTime" HeaderStyle-HorizontalAlign="Left">
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:BoundField>
                                    <asp:BoundField HeaderText="File" DataField="FileCName" NullDisplayText="no file" />
                                    <asp:BoundField HeaderText="FilePath" DataField="FilePath" Visible="false" />
                                    <asp:TemplateField HeaderText="Show" HeaderStyle-HorizontalAlign="Left" Visible="true">
                                        <ItemTemplate>
                                            <asp:ImageButton ID="bthshow" runat="server" ImageUrl="~/Images/btnshow.jpg" CommandArgument='<%#Eval("FilePath") %>'
                                                CommandName="download" ToolTip="show" Width="35px" Height="25px" />
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:TemplateField>
                                    <asp:TemplateField HeaderText="Delete" HeaderStyle-HorizontalAlign="Left">
                                        <ItemTemplate>
                                            <asp:ImageButton ID="btndelete" runat="server" ImageUrl="~/Images/close-button.gif"
                                                CommandArgument='<%#Eval("AutoId") %>' CommandName="deleted" ToolTip="show" Width="35px" Height="25px" />
                                        </ItemTemplate>
                                        <HeaderStyle HorizontalAlign="Left" />
                                    </asp:TemplateField>
                                </Columns>
                                <AlternatingRowStyle BackColor="White" HorizontalAlign="Left" />
                                <EditRowStyle BackColor="#2461BF" />
                                <FooterStyle BackColor="#507CD1" ForeColor="White" Font-Bold="True" />
                                <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" HorizontalAlign="Left" />
                                <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
                                <RowStyle BackColor="#EFF3FB" HorizontalAlign="Left" />
                                <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
                                <SortedAscendingCellStyle BackColor="#F5F7FB" />
                                <SortedAscendingHeaderStyle BackColor="#6D95E1" />
                                <SortedDescendingCellStyle BackColor="#E9EBEF" />
                                <SortedDescendingHeaderStyle BackColor="#4870BE" />
                            </asp:GridView>

.CS Code

if (e.CommandName == "download")
            {
                string filename = e.CommandArgument.ToString();
                if (filename != "")
                {
                    string path = MapPath(filename);
                    byte[] bts = System.IO.File.ReadAllBytes(path);
                    Response.Clear();
                    Response.ClearHeaders();
                    Response.AddHeader("Content-Type", "Application/octet-stream");
                    Response.AddHeader("Content-Length", bts.Length.ToString());

                    Response.AddHeader("Content-Disposition", "attachment;   filename=" + filename);

                    Response.BinaryWrite(bts);

                    Response.Flush();

                    Response.End();
                }
            }