Hello. This shows up when trying to add tags to a headline with org-ctrl-c-ctrl-c:
apply: Wrong type argument: listp, org-tags-completion-function Org-mode version 8.3beta (release_8.3beta-1045-gd8494b @ /usr/local/share/emacs/site-lisp/org/) GNU Emacs 24.5.50.1 (i686-pc-linux-gnu, GTK+ Version 3.4.2)