Incomprehensible upstart error messages

I ran "service ssh restart", and got the following error message:

restart: Rejected send message, 1 matched rules;
type="method_call", sender=":1.75" (uid=1000 pid=3409
comm="restart) interface="com.ubuntu.Upstart0_6.Job"
member="Restart" error name="(unset)" requested_reply=0
destination="com.ubuntu.Upstart"
(uid=0 pid=1 comm="/sbin/init"))

It turns out this is how Upstart (Ubuntu's init(8) replacement) says "you're not root".