Static IP (single IP address)

I have 2 Comcast Business Gateway Routers. One has a block of 5 address and I had no problem getting it to pass traffic back to where it should go on the private network.  The other has a single static IP and, even though I configured it exactly like the router with 5 addresses, it refuses to pass traffic through. It just displays the router's login screen.

I think it's not working because the mapping in the 1-to-1 NAT section is not enabled but it will not allow me to enable it. I go to check the "enable" box and the router resets but the checkmark never sticks.