Ok, I reinstalled everything and tried again. Same issue.
But I noticed that I have two different behaviours between the two CDU. I post the screenshot.
The capt's CDU lets me put ELMOX to the scratchpad and then blocks the LSK1L, the FO's CDU sends an INVALID ENTRY as soon as I click on ELMOX.
This is the same for any actions I try to perform, for instance changing the arrival rwy or changing the cruise altitude. Instead, I was able to change the transition level at LOWI.
Very, very strange...
I really don't believe that this depends on Prepar3d (everything else is working perfect), maybe I make some mistakes, I don't know.
I can't open a ticket, but maybe someone at PMDG may want to try to help. I really would appreciate it.
I have Win 7 Pro 64, FSUIPC registered version, and the NGX. Nothing else.
Thank you.