Dual Duos on Same Network?

I recently acquired an older [i.e. legacy] Duo to perform some simple backups.  While working on configuring it, I've had to setup a separate LAN using a different router.  Once configured for my main LAN, I connected it to my main LAN and re-booted it.  Oddly, I'm seeing zero sign of its existance on the main LAN- no ping responses, no sign of it using RAIDar, no response at all.  I'm sure you're going to tell me that this is a network thing, but I've exhausted a lot of ideas as to why this isn't appearing and I'm beginning to wonder if there's anyway that having two readynas Duos on the same network could possibly be an issue? 

I have all of my NAS devices setup with a fixed IP address, all in the same range, and all with the same subnet etc- it really should work, but it's disappearing on my LAN unless and until I connect it to this simple LAN that I setup on the side.  When I do that- it connects and appears all correctly.

Anyone have any thoughts on this?

Thanks.

I guess I'll try setting it up as DHCP and see if I can get it to appear that way...