BuddyPress.org

Why did you uninstall SI captcha?

SI CAPTCHA Anti-Spam works with WordPress 2.6+, WPMU, and BuddyPress

https://wordpress.org/extend/plugins/si-captcha-for-wordpress/

WP-reCAPTCHA is not up to date for BuddyPress 1.1, that is why it does not work.