Unable to modify administrative settings after El Capitan upgrade
If you are using Centrify, then this thread led me to this Apple forums answer: let the system rebuild the authentication database:

sudo mv /var/db/auth.db /var/db/auth.db.old


and restart. This fixed all the related privilege escalation failures for me and I seem to recall a Centrify upgrade was supposed to be done before the Mavericks upgrade too.

It has not, however, re-enabled network user logon. The check-box to allow network user logon is missing from Users &amp; Groups still.