Well sometimes things like these happen its just sometimes every add-on it's effected in a different way. I have a 737 from another developer and i cannot start the engines if i go to the default cessna or 737 default and switch the engines off and then go to the 737 (add-on), then I have another 737 from another developer that I can set from cold and dark so I go in this aircraft and then I go into my other 737 (add-on) and it starts fine but when I went on the forum they dont have the problems that i have.Anyway good luck.