i'm having a similar problem, do you have groups disabled in buddy press?
the media component would not activate if i had them disabled, and if i enabled them it would activate ok. However, if i then disabled groups after activating the media component it completely locks out the whole wordpress installation!! i cant even log in to re-activate groups, and i had to completely delete the whole shooting match and start again.....
so don't do that!!
i'm using wordpress SU 3.0.1 so might be a little different for you?