I am running into a similar issue. I first installed bbPress, then discovered that my site needed a few BuddyPress features.
During initial BuddyPress installation, I did not activate the forums, since I already had those. A page for forums was not created.
Then, I looked here and found the guide to install site-wide forums, which is what I want. The problem was that my forums page was nowhere to be found.
After installation, however, where it is detected that bbPress is already installed, I have this situation:
1. Forums still don’t show up in the links where “Activity” and others are shown.
2. According to this:
Note: During the Installation Wizard, Forums will be associated with the “Forums” page. In some installations, you do not need to change anything. But if your sitewide forums won’t work, go to wp-admin BuddyPress > Pages and you’ll find the association and remove the Forums Page as the selected page.
not having an associated page is the right way to go. This gives me the error message that an association should take place, but I guess that’s a contradition we’ll have to live with.
