I'm having the same problem after upgrading to 3.4
Not working for me. I get the default contact form 7 error when submitting and no email is sent.
Tried deleting and reinstalling contact form 7
Tried reinstalling the update to 3.4
Tried disabling Contact Form to DB Extension and all other extension
(the form data does make it into the DB with Contact Form to DB Extension)
Tried disabling all other extensions. (my site has only 1 other WP No Category Base - WPML compatible)
Unsure if other emails are being sent or not
Any things to try?