Hi samsmuthu,

Check this example. Now please take its reference and correct your code.

HTML

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
    <asp:UpdatePanel ID="UpdatePanel3" runat="server">
        <ContentTemplate>
            <asp:Button ID="BtnShow" runat="server" Text="Show" />
            <asp:Button ID="btnDownload" runat="server" Text="Download" OnClick="DownloadFiles" />
        </ContentTemplate>
        <Triggers>
            <asp:PostBackTrigger ControlID="btnDownload" />
        </Triggers>
    </asp:UpdatePanel>
    <asp:UpdatePanel ID="UpdatePanel4" runat="server">
        <ContentTemplate>
            <asp:GridView ID="GridView2" runat="server"
                AutoGenerateColumns="false" AllowPaging="true"
                OnPageIndexChanging="GridView1_PageIndexChanging"
                PageSize="25" CssClass="GridViewStyle"
                EmptyDataText="No files available">
                <Columns>
                    <asp:TemplateField HeaderText="" ItemStyle-Wrap="false" ItemStyle-VerticalAlign="Middle" ItemStyle-HorizontalAlign="Left">
                        <ItemTemplate>
                            <asp:CheckBox ID="ChkSelect" runat="server" />
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="File name" ItemStyle-Wrap="true" ItemStyle-VerticalAlign="Middle" ItemStyle-HorizontalAlign="Left">
                        <ItemTemplate>
                            <asp:Label ID="LblNewPhotoFileName" runat="server" Text='<%# Eval("NewPhotoFileName")%>' Visible="true"></asp:Label>
                            <asp:Label ID="LblPhotoFilePath" runat="server" Text='<%# Eval("PhotoFileName") %>' Visible="false"></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Photo" ItemStyle-Wrap="false" ItemStyle-VerticalAlign="Middle" ItemStyle-HorizontalAlign="Center">
                        <ItemTemplate>
                            <asp:Image ID="ImgPhoto" runat="server" BorderWidth="1px" Style="max-width: 150px; max-height: 100px;" Visible="true" ImageUrl='<%# Eval("PhotoFilePath")%>' />
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>
        </ContentTemplate>
    </asp:UpdatePanel>
</asp:Content>

Namespaces

C#

using System.IO;
using Ionic.Zip;
using System.Collections.Generic;

VB.Net

Imports System.IO
Imports Ionic.Zip
Imports System.Collections.Generic

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        string[] filePaths = Directory.GetFiles(Server.MapPath("~/Files/"));
        List<ListItem> files = new List<ListItem>();
        foreach (string filePath in filePaths)
        {
            files.Add(new ListItem(Path.GetFileName(filePath), filePath));
        }
        GridView1.DataSource = files;
        GridView1.DataBind();
    }
}
protected void DownloadFiles(object sender, EventArgs e)
{
    if (!Directory.Exists(Server.MapPath("~/New/")))
    {
        Directory.CreateDirectory(Server.MapPath("~/New/"));
    }
    using (ZipFile zip = new ZipFile())
    {
        zip.AlternateEncodingUsage = ZipOption.AsNecessary;
        zip.AddDirectoryByName("Files");
        int i = 1;
        foreach (GridViewRow row in GridView1.Rows)
        {
            if ((row.FindControl("chkSelect") as CheckBox).Checked)
            {
                string filePath = (row.FindControl("lblFilePath") as Label).Text;
                File.Copy(filePath, Server.MapPath("~/New/") + "Block_" + i + Path.GetExtension(filePath));
                zip.AddFile(Server.MapPath("~/New/") + "Block_" + i + Path.GetExtension(filePath), "Files");
            }
            i++;
        }
        Response.Clear();
        Response.BufferOutput = false;
        string zipName = string.Format("Zip_{0}.zip", DateTime.Now.ToString("yyyy-MMM-dd-HHmmss"));
        Response.ContentType = "application/zip";
        Response.AddHeader("content-disposition", "attachment; filename=" + zipName);
        zip.Save(Response.OutputStream);
        Directory.Delete(Server.MapPath("~/New/"), true);
        Response.End();
    }
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        Dim filePaths As String() = Directory.GetFiles(Server.MapPath("~/Files/"))
        Dim files As New List(Of ListItem)()
        For Each filePath As String In filePaths
            files.Add(New ListItem(Path.GetFileName(filePath), filePath))
        Next
        GridView1.DataSource = files
        GridView1.DataBind()
    End If
End Sub
Protected Sub DownloadFiles(ByVal sender As Object, ByVal e As EventArgs)
    If Not Directory.Exists(Server.MapPath("~/New/")) Then
        Directory.CreateDirectory(Server.MapPath("~/New/"))
    End If
    Using zip As ZipFile = New ZipFile()
        zip.AlternateEncodingUsage = ZipOption.AsNecessary
        zip.AddDirectoryByName("Files")
        Dim i As Integer = 1
        For Each row As GridViewRow In GridView1.Rows
            If (TryCast(row.FindControl("chkSelect"), CheckBox)).Checked Then
                Dim filePath As String = (TryCast(row.FindControl("lblFilePath"), Label)).Text
                File.Copy(filePath, Server.MapPath("~/New/") & "Block_" & i & Path.GetExtension(filePath))
                zip.AddFile(Server.MapPath("~/New/") & "Block_" & i & Path.GetExtension(filePath), "Files")
            End If
            i += 1
        Next
        Response.Clear()
        Response.BufferOutput = False
        Dim zipName As String = String.Format("Zip_{0}.zip", DateTime.Now.ToString("yyyy-MMM-dd-HHmmss"))
        Response.ContentType = "application/zip"
        Response.AddHeader("content-disposition", "attachment; filename=" & zipName)
        zip.Save(Response.OutputStream)
        Directory.Delete(Server.MapPath("~/New/"), True)
        Response.End()
    End Using
End Sub