@sunshineusa 

I am not quite sure I understand what you mean by privacy seperator.  Can you clairfy? Is is the isolation feature for Guest Networks so they can't communicate with the main network?

@sunshineusa 

Is your printer on your Guest Network?  If so likely the privacy seperator is that you are isolating the Guest from your main network, making it impossible for the devices to see each other.  Another possible issue could be Double Nat.  Who is your ISP and what is the device the main deco connects to?

@sunshineusa 

Double NAT happens when your modem is actually a modem/router or a gateway device and your network traffic gets translated through 2 private LAN networks, one at the Deco and One at the gateway before going out to the internet or public network.  Can you provide us the Make and model of the modem so we can confrim if this is an issue or not?  Since the guest network isn't being used the issue could potentially be with the Deco's single network routing technology and may have trouble communicating with the Deco's single network design.  To rule this out try turning on your Guest network but only for the 2.4 GHz network.  Make sure you allow the Guest network to see the main or host network.  Then test.  If successful the issue will be confrimed that the printer is having issues working with a single network desgin and you can keep this setup to ensure functionality.  If it does work you can also contact your printer maker to see if they have a potential fix. 

If it doesn't work then we can contact enigeering and see if anything else can be done.  At that point we would need to know the what the modem make and model is, what the printer make and model is, what firmware both devices are running.