Upgrade to 2.3.0.1 breaks server

Hi

I've upgraded dovecot from 2.2.22 to 2.3.0.1, and now I can't log in any longer. My mail client says that the user name and password are rejected by dovecot. I get this messsage in the system logs:

% journalctl -u dovecot.service (...) Mär 03 01:39:23 desktop systemd[1]: Stopped Dovecot IMAP/POP3 email server. Mär 03 01:39:23 desktop systemd[1]: Started Dovecot IMAP/POP3 email server. Mär 03 01:39:39 desktop auth[5736]: PAM audit_log_acct_message() failed: Operation not permitted

I've followed the instructions in https://wiki2.dovecot.org/Upgrading/2.3 and https://repo.dovecot.org/ (for Ubuntu Xenial).

Any ideas..?

Bye V.W.