Just found out:
All in one SEO brakes: https://bbpress.org/forums/topic/all-in-one-seo-pack-error/
I unpublished SEO plugin and Forum started working.
Hi there, I am getting exactly the same issue and I tried to fix but I only get that message “You are not allowed to edit posts in this post type.” – http://prntscr.com/aux1nl
Any advice is welcome.
Thank you.