It's sounds strange, but I discovered yesterday that I could not find the PMDG 777-300ER Expansion in the FSX aircraft list, even though the PMDG Operations Center reporting ok for the 777-300ER Expansion after udate?
So after reinstall PMDG 777-300ER Expansion the problem with "PMDG_737NGX_2.dll APPCRASH when closing FSX" disappeared!
Jan Persson