I did a complete re-install (deleted all pp_ tables from the database, deleted all files/folders, removed all cookies from local machine - then completely re-installed).
I have the identical problem. Users can log in and see ads, and can post Quick Replies all day long. No user - the original poster, the system admin, moderators or registered users - can post comments using the Comments link and the WYSIWYG editor. No matter who tries, the result is the same - Did not Complete All Required Fields. Problem is, there are no fields other then the main comment box....