I also get this same issue (does not show the list of members in my ward and does not outline my ward) as well as the same "GET
https://www.lds.org/rcmaps/services/units?lang=eng 500 Internal Server Error" error with both Firebug and Chrome Dev Tools.
My calling is Ward Website Administrator.
This works (outlines my ward and shows me the list of members) on the non-beta version at lds.org/maps, but does not work at the lds.org/rcmaps version.