Thanks Rokas that was the problem!
If i can ask another question.. If i use a spline that is not flat no Z, but rather has a more topographic reality where its not flat but has up and downs, how can i make my buildings vertical and not to shift their z axis alignment to follow the normals of the curve. The same thing you can do in Forest pack for the trees with a slider so they can follow the surfaces normals or keep to vertical.