lost password form broken

getting the following error on my lost password page:

Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘sweetcaptcha_lost_password_form’ was given in …/wp-includes/plugin.php on line 406

Using wp version 3.5, plugin version 2.4.3.5 (same error in previous version), and “Enable SweetCaptcha for lost password form.” is enabled.

I grepped through the plugin code and found the add_action line, but couldn’t find function named “sweetcaptcha_lost_password_form”. Here’s the grep:

grep -R sweetcaptcha_lost_password_form *
sweetcaptcha.php: add_action( ‘lostpassword_form’, ‘sweetcaptcha_lost_password_form’, 1 );

https://www.ads-software.com/extend/plugins/sweetcaptcha-revolutionary-free-captcha-service/