XScreenSaver (and probably most other third-party) screensavers no longer work, because, for some reason, Apple decided that screensavers should be dynamically loaded into the screensaver application rather than be separate applications, and they decided to make the screensaver application be 64-bit (because of the massive numbers that screensavers deal with?) which means that all the old 32-bit screensavers can no longer be loaded.