Misson add-on never has the plane

I just started downloading tonight and the three missions I have downloaded, unzipped, then did exactly as the README folder told me. When I launch FSX on my Gateway FX-6831 and go to missions they are there in the lists and when I hit fly mission an error comes up and says there is no plane file or another error and I end up flying in the propeller plane that looks like a kite. It is the first plane you get really with the propeller right behind where the pilot sits. Please help me figure this out I love the idea just wish it worked better.