Someone reported a conflict between one of my plug-in and yours - the reason was line 52 in sweetcaptcha.php (v188.8.131.52):
wp_enqueue_script( 'jquery-ui.custom', plugins_url( 'js/jquery-ui.custom.min.js', __FILE__ ) ); // v1.9.2 - 2012-11-27
I also noticed (though it wasn't breaking anything) that it was directly inserting its own jQuery file on log-in pages (library/public.php). WordPress now comes bundled with jQuery & jQuery UI, and using them via the
wp_enqueue_script() can avoid a lot of plug-in conflicts. Would you mind updating your plug-in to use them?