I had to reconfigure my home network from 192.168.2.0/24 to 192.168.0.0/24 in order to support some IPsec policy exclusion stuff.  In the process, my MN-500 decided to stop forwarding packets from the Internet to the server.  Even after a reboot, it still was not happy.  I ended up removing the port forwarding rule, re-adding it and then everything was fine.