BuddyPress.org

Forgot to mention that you’re missing a do_action in your display_recaptcha_bp() function.

Based on the code you’re using, that code is:
do_action( 'bp_captcha_errors' );

You should also remove the WPMU check since BP works on standard WP circa v1.2.

I’ve amended your code here:
http://pastebin.com/QCbxXvhh (untested)

Also, Peter, did you ask the original author of the plugin for permission before attempting to fork it? It’s just a courtesy thing.

If I did what you did, I could have released a thousand plugins by now! Okay maybe not a thousand but you get my point!