it could be a theme or plugin issue
As a test switch to a default theme such as twentyfifteen, and see if this fixes.
If that doesn’t work, also deactivate all plugins apart from bbpress and see if this fixes. if it does, re-enable one at a time to see which is causing the error.
Then come back
Thank you for your quick reply.
It was the theme. Unfortunately, this theme by ThemeMove rejects all forum plugins in one form or another.
It’s very frustrating.
Thank you for your help!