BuddyPress.org

I had the same problem, and after hours of playing with it the only solution was to disable all plugins, create the blog by using the dashboard create new blog,

The problem is one of the plugins – not pointing any figures at BP, doesn’t allow the sql to fire and create the tables in the database.

Once the blog is working, you may have errors floating about the screen but just ignore them till you have a theme activated for that new blog, and then turn on all the plugins back on.

Convoluted yes, but it works for me.