Error 500: Incorrect authentication data when sending e-mail

[nsns]

Hello.
I have setup a personal e-mail account.
The test connection and send test e-mail works ok.
The incoming mails also works ok
But when i try to send a e-mail i get the error
Error 500: Incorrect authentication data,
How can i resolve this?
Kind regards.

[emillod]

What kind of mail server you're using? Gmail? Something else?

[nsns]

imap with cpanel hosting
I have a lot of e-mail accounts in this installation and only in one e-mail account i have this problem.
The problematic account was disabled for some time and now i enable it again. The password is correct.