BuddyPress.org

Ah… the famous “there was an error when creating the topic” problem.

Go to your site, and go to a group than you have individually created. (important!)

Go to groups admin –> Group Settings

Now see the little checkbox “enable discussion forum”?

Un-check it, than recheck it, and go to the bottom and click “save”

Try to create new topic now.

(all credits of Hnla for the solution)