This is exactly what I have had. I created another thread about this. What happened in my case was that after updating from WPMU 2.8.x <2.8.9 to the latest WPMU 2.9.1 I still get a fatal error. However it doesnt say anything about not being able to redeclare bp_loader_activate() any more it just says fatal error like I have highligthed in my other post.
