Stream St = File.Open(Server.MapPath("/UPLOAD/UPFILE.DOC"),FileMode.OpenOrCreate);
==>
Stream St = File.Open(Server.MapPath("./UPLOAD/UPFILE.DOC"),FileMode.OpenOrCreate);
==>
Stream St = File.Open(Server.MapPath("./UPLOAD/UPFILE.DOC"),FileMode.OpenOrCreate);
或者是
Stream St = File.Open(Server.MapPath(@"/UPLOAD/UPFILE.DOC"),FileMode.OpenOrCreate);