Topic: Errno::ENOENT (No such file or directory - /assets/)

Hi all,
In production env (ONLY),  deployed at heroku, after adding a mailer component sending email via gmail (following all the best practices),  heroku generate the following error:

Errno::ENOENT (No such file or directory - /assets/):

after the rendering of the mailer template action. (but email wasn't sent) I didn't find anythig like around the web.

Any ideas?