Twice I uninstalled FSX, removed all the corresponding folders, start FSX to create new folders and then installed SP1. And twice from every FSX aircraft I could only see one livery from one model.So I could see one Cessna 172SP and one Cessna 172SP G1000, etc.Also when I installed the BeaverX I got the same problem.Have anybody out there the same problem or even better a solution for this problem

Yes I had the same problem and yes I found the solution. Re-Click the "Show all variations" checkbox at the bottom of the "Select Aircraft" menu.FSX default behavior is to not show all variations, and by installing SP1 through a "clean" install and new FSX.cfg file, you revert to default behavior.