Downloading csv files with zip?

I have this codes, the problem is, whenever I press the download button, it gives an error indicating Directory Not Found. I have already an upload function with the following fileUpload.PostedFile.SaveAs(Server.MapPath("~/Upload")); Below is my codes:

protected void Page_Load(object s开发者_如何学编程ender, EventArgs e)
{
    if (!IsPostBack)
    {
        var files = Directory.GetFiles(@"~/Upload");
        gvFiles.DataSource = from f in files
                             select new
                             {
                                 FileName = Path.GetFileName(f)
                             };
        gvFiles.DataBind();
    }

}

protected void btnDownload_Click(object sender, EventArgs e)
{

    string fileName = string.Empty;
    string filepath = Request.MapPath("~/Upload");
    string downloadFileName = "Attendance.zip";
    Response.ContentType = "application/zip";
    Response.AddHeader("content-disposition", "filename=" + downloadFileName);

    using (ZipFile zip = new ZipFile())
    {
        foreach (GridView row in gvFiles.Rows)
        {
            CheckBox cb = (CheckBox)row.FindControl("chkSelect");
            if (cb != null && cb.Checked)
            {
                fileName = (row.FindControl("lblFileName") as Label).Text;
                zip.AddFile(Server.MapPath(Path.Combine(filepath, fileName)), "");
            }
        }
        zip.Save(Response.OutputStream);
    }
}

Can anyone help me with this please? When I use Directory.GetFiles(@"~/Upload"), I get the mentioned error

var files = Directory.GetFiles(Request.MapPath("~/Upload"));