P & N 3.1b and loading existing players

[dumbluck]

Ah-HA!

.emp files created in vanilla SE4 will not work in P&N. SJ added some racial techs, and because of that the .emp files are incompatable.

To fix this:
Start a new game, with just yourself and a high number of random AIs. Then switch to each AI and save the Empire File. Under the uppermost, farthest left hand button in the menu is both the "players" button for switching players and the "save empire" button, which is self explanatory.