In few of the latest versions, root login through SSH has to be explicitly allowed but it should work through Console. Any other username should also work fine. If this is not the case then password reset is the only option.
I got the same error when I got my new device. Called technical support and was told that by default, GUI was disable during initial set up. However, on the quick start guide, it was not mentioned and misled to use the RJ-45 cable to connect. I finally got a serial to usb cable and connect the adapter to get on it.