I'm 99% sure you did not configure something correct.
I have multiple port forwards enabled, including SSH, multiple Minecraft servers, SIP ports, Web servers, etc.
Make sure you pick the correct option for UDP/TCP, make sure you set up a reservation for the IP of the host you want to connect to on the LAN, and lastly, remember you can usually not connect out and back in through the same connection, so don't do the testing of the external connection from the same network as where you remote machine is.