Comment 2 for bug 930266

Had that exact same problem on Ubuntu 15.10.

The File /etc/apparmor.d/usr.sbin.ntpd contains the following line:

  # samba4 ntp signing socket
  /{,var/}run/samba/ntp_signd/socket rw,

But the line should be

/var/lib/samba/ntp_signd/socket rw,