I am getting this error after updating to dovecot2-2.2.26.0_1 under FreeBSD 10.2 when a user tries to login via roundcube webmail. I am able to login via my own mail client and there is no error in the log when roundcube fails to login.

I stopped dovecot, removed all the dovecot files from the maildir folders and restarted dovecot, but get the same error.

https://help.directadmin.com/item.php?id=473