Question2Answer Fatal Error - Could not sent email confirmation

When user try to verify email, after tapping confirm button in mysite.com/confirm, it says-

Question2Answer fatal error:

Could not send email confirmation

Stack trace:

require() in index.php:27
require() in qa-index.php:188
qa_get_request_content() in qa-page.php:47
require() in page.php:183
qa_send_new_confirm() in confirm.php:62

how to solve it? please help him. Email confirmation code is not sending