[Plugin: Contact Form 7] "Failed to send your message."

Despite all the topics on that issue, i can’t figure out why CF7 returns the “Failed to send your message.”

– I don’t have Askimet activated.
– Feedback is not marked as spam.
– I don’t have any “Super-Cache”
– WP_mail is working fine alone.

Any help appreciated.

Thanks

http://wordpress.org/extend/plugins/contact-form-7/