Re: forum does not work
Make sure that you have deactivated all other plugins except BuddyPress. Or better yet, remove them from your plugins directory. And then try to reinstall the BuddyPress forums again.
Or, install a shiny new version of WP/BP in another subdirectory with a fresh database to see if you still experience the forum error. That will help you to at least isolate the issue. It’s pointless to troubleshoot something after you’ve added other plugins and customizations to the mix.