Well, I was selecting the Terrain Node with a high hill and put to generate the navmesh, and the SDK was crashing. Now I have properly selected a node that contains all terrain, doodads, structures and everything else and properly works.
Sometimes it crashes the SDK, even selection the parent node, even with the same parameters it crashed and, after restarting the SDK, it did not. But besides that, tweaking the parameters a bit generates a good mesh indeed =]