[Resolved] Can't send an encrypted mail

When I want to send an encrypted mail or answer, (I’ve installed openkeychain, I can read encrypted mails I receive, …) I’ve an error : failed sending : null (envoi en échec : null).

But if I desactivate encryption, I can send my email.

Do you have any idea to fix this bug ?

I finally find something :
Go to the account file, select a long time to access to the account settings.
Select cryptography, my key, and clic on “use my key”.

It’s run for me.