I have a problem with FSX that is getting on my nerves, 99% of all custom freeware aircrafts i add to my FSX display as this in aircraft selection and also in-game:

So the whole plane is all white. Epic fail. Any ideas ?
I add all planes to Microsoft Flight Simulator X/SimObjects/Airplanes, I have Vista 64-bit with 4gb of ram and Sapphire HD4870 X2 graphics. And I have tried over 40 aircrafts >_>
SAC