Q: Cannot add a new shared folder

When I try and add a folder (click +) and select a folder, it does not appear in the list. The pop up window closes, but the folder does not appear in the list. I have tried with multiple folders and am not able to add any. I am logged in as an administrator, and am using OS X El Capitan version 10.11.4 on an iMac Retina 5K, 27 inch, Late 2014 (in case any of that is useful).