I took a look and you currently have two users on your blog - https://maickcosta.wordpress.com/wp-admin/users.php .
That error message does indicate that there is no user registered to the email address that you entered.
We haven't received any other reports of this so it sounds like it is limited to your experience. That in mind, please double check with the user and make sure that they do have an account and that you have the correct email address.
If you continue to encounter this issue, please let us know. Please do not post the user's email address in the public forums.