port forwarding does not work

I tried selecting a device and add a port, the device is online with a fixed IP address, port forwarding app says no device assigned and selects the wrong ip address for the device.  This is very frustrating, I have port forwarded on several gateways and never had an issue, this is a brain dead modem!  I am using the "panoramic wifi app" and DAR168C gateway.  Not being able to directly access the gateway is ridiculous.