Make sure you are logged in to your computer with admin priviledges. That detail frustrated me because in general I avoid day to day use with admin priviledges. Sys pref:users_groups is where you chek that.
Bingo! Thank you, Will... that was it!
I, too, keep my admin powder dry, even though it can be easy for me to forget all the implications.
I might also add... "frustrated" very aptly describes my previous outlook on this problem, just as much as "grateful" describes my appreciation of your good advice.