[Plugin: Sweet Captcha] error w admin notices

On multisite this plugin throws errors :

Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'sweetcaptcha_admin_notices' was given in /home/admin/domains/portaljumper.com/public_html/wp-includes/plugin.php on line 403

for now this hack will do, but problem remains in code:
REMOVE the following line from the main plugin file

// Add admin notices.
add_action('admin_notices', 'sweetcaptcha_admin_notices');

http://wordpress.org/extend/plugins/sweetcaptcha-revolutionary-free-captcha-service/