Umberto,
So since KORD worked, I installed KFLL, KDFW and KLAX all worked fine.
I also installed KIAH, which however gave me the "The trial period for KIAH has started" and the airport was missing all the buildings.
I will download the installer again and try to reinstall into P3Dv4 tomorrow. Will let you know what happened.
Thanks
Juergen Mader