I was searching first in the forums for a problem like mine. Found like 2 post but none of them provided me a solution.
So i write here in order to get an answer and finally play like i would like to. Because i really love this game, and i usually play with my pals (eventhough we are a bit too old for this )

So we tend to play multiplayer custom battles. And we found that there we couldn't use all the nations. Especially my beloved Kingdom of Jerusalem. I found someone that said that if we changed the nations order on "descr_strat", they would appear. But no, no Jerusalem was found.

We play Stainless Steel 6.4 and if you guys need more information in order to play with these nations on custom battle, just ask for it.

May the Medieval Gods bless our battles and absolve us of any lagg in our way.