Rather than invoking init scripts through /etc/init.d, use the service(8)
utility, e.g. service isc-dhcp-server restart

Since the script you are attempting to invoke has been converted to an
Upstart job, you may also use the stop(8) and then start(8) utilities,
e.g. stop isc-dhcp-server ; start isc-dhcp-server. The restart(8) utility is also available.
start: Rejected send message, 1 matched rules; type="method_call", sender=":1.91" (uid=1000 pid=6550 comm="start isc-dhcp-server ") interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply="0" destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")