Unable to SSH into computer unless logged in locally

Unable to SSH into computer unless logged in locally

I've set up Remote Login on a Mac Mini running 10.8.4. After configuring
port forwarding on my router, I'm able to SSH into this computer, whether
from an external or internal computer.
From what I've read, it seems like the SSH server is set up to run at
boot. But the problem is that if no one is logged in locally, I cannot SSH
into the computer. The connection simply times out. Although I've
authorized SSH access (via password) to only one of the administrators, it
doesn't seem to matter who is logged in.
Does anyone know how to allow SSH access without needing a local user to
be logged in?
Thanks!