PMDG 777 shell of an aircraft

I had the same issue because I tried to alter the aircraft registration in the plane select menu. Leave it as is and it should be fine. PMDG said the software needs those numbers in order to properly run the program. Hope that helps.

There are files for each livery in a subdirectory of FSX>PMDG>PMDG 777 that go by tail number.  It has many settings for that particular plane.  Probably if there is no file corresponding to the tail number of your livery, many settings won't load.

Mike