So you have a server on your local network that you can access anywhere in the world. With a new NAT router, after port forwarding, you can still access it from the internet, but not from inside the local network. After looking around, you found out that the router does not support NAT loopback.
This happend to me recently when I switched my ISP to Telus, with their NAT router and modem also double as TV modem, it has to be my gate way NAT. Without loopback, not being able to access my local servers from the public ip address was beyond annoying. Untill something in the router configuration hit me - hack the DNS: