download file in asp.net

--------------------------------------------------------------------
protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
    {
        string filename = "~/Safelife Brosher.zip";

        if (filename != "")
        {

            string path = Server.MapPath(filename);

            System.IO.FileInfo file = new System.IO.FileInfo(path);

            if (file.Exists)
            {

                Response.Clear();

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

                Response.AddHeader("Content-Length", file.Length.ToString());

                Response.ContentType = "application/octet-stream";

                Response.WriteFile(file.FullName);

                Response.End();

 
             
            }
               

            else
            {

                Response.Write("This file does not exist.");

            }
        }
    }
-----------------------------------------------------------------------