FSX Ultra High Graphics

I have a question for the computer nerds and geeks who may be flight sim people, How come I can fly my missions on Ultra High Graphics with the aircraft setting at Medium High and then switch to Free Flight and not be able to fly at all?
If anyone knows the answer to this perplexing puzzle please post an answer on the forum, I'm stumped as to the reason for this lack of ability to fly in Ultra High Graphics with even a Medium High setting on the aircraft.
I can fly the sim with Ultra High settings on the aircraft but not the Graphics, I like FSX much better because of the missions, but having FS 9, and being able to fly with all the settings maxed out and still having no problems, leads me to believe that it is not my computer but the program itself that is the cause of this problem.
Thanks for any help!