BuddyPress.org

I found a solution to this problem here:

https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/bbpress-posting-errors-missing-database-tables/

Check your database tables and make sure all of the necessary tables for bbPress have been created in your installation. In my case I was missing the bb_post table (the one involved in actually posting a topic) – it was failing to install properly due to an error in MySQL syntax – all explained in my thread. By downgrading my MySQL version I was able to install bbPress succesfully – the missing table (bb_post) was created and I was then able to post forum topics in my groups without any error!