Hi 100asa
I assume you are using the 'AsK a Question' plugin - if so then in modules/pages/ask_a_question/header_php.php replace line 43
Code:
  if ($zc_validate_email and !empty($enquiry) and !empty($name)) {
with these two lines
Code:
  $zco_notifier->notify('NOTIFY_CONTACT_US_CAPTCHA_CHECK');
  if ($zc_validate_email and !empty($enquiry) and !empty($name) and $error == false) {
Hope this helps/works
Regards