BuddyPress.org

Don’t know if this is the same case for others, but I found that my bb-config.php file had a couple of empty lines at the end, which was causing a 404 error when posting a group or a topic in a forum.

Once I removed those extra blank lines all worked great.

Firfox led me to the answer by stating that the headers had already “started” in the bb-config.php file.