[biberkopf]

I had the same problem. I disabled WP User Avatar which solved the problem.

This plugin is apparently not compatiple with BuddyPress. The FAQ for the plugin says:

Will WP User Avatar work with BuddyPress?
No, BuddyPress has its own custom avatar functions and WP User Avatar will override only some of them. It’s best to use BuddyPress without WP User Avatar.