I spent many hours recently looking into this again. The problem with the post or comments box not showing up is only for events which are set for groups. The events which are not attached to groups can be commented on by those going to the event. I have checked every single permissions on pages, blocks, and navigation. You have to be the site administrator to make the initial post in events which are designated for specific groups. I still have not found a solution. When I enable the info for who can post, I get an error (see attached image).