What's the problem Justin Timberlake?

Justin Timberlake looked very mad on the film set of his new movie "The Social Network", in Los Angeles this weekend. We are wondering why, is he having problems with girlfriend Jessica Biel or is he just tired of filming? Come on Justin! Stop worry be happy it's just a film set! We hope that Justin gets back on track very soon and starts smiling again. We like him better that way!