I think, in my case, it’s due to the fact that I erased some picture via FTP while it was still accounted in the WordPress DB. Had to reinstall everything.
Having the same issue in WP 4.1. Library won’t load in grid view, be it through Media > Library, the text editor or a plugin. It makes the modal window for media insertion useless and there’s no way around it.
edit : A ticket about this exact bug in WP 4.0.
