BuddyPress.org

Well if all you did was change a theme in the first place, try changing it back and see if that solves it. If it does, you’re a step closer to working out the solution. It might be something simple like a lack of support for it in the new theme. All you’d have to do would be to cut and paste the info from the old theme (which must be newer and did support it) into the new one (which is probably old and was designed before activity streams were invented). Let us know how this goes!