I have to download an uploaded file and i have the following code,it has some errors...can anyone give a proper suggestion .

protected void gdvfile_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName == "Download")
            {
                var a = e.CommandArgument.ToString();
                string filename = a;
                Response.AppendHeader("Content-Disposition","attachment;filename=" + filename);
                string aaa = Server.MapPath("~/Upload/" + filename);
                Response.TransmitFile(Server.MapPath("~/Upload/" + filename));
                Response.End();
            }
        }