I'm having the same problem. After I installed the Phoenix 5.5 sim updates, when I try to choose a flite test plane, it stalls the sim for awhile. When it actually loads, all I get is a white 3-D model. The thumbnail icon also has a question mark.It does fly, but it doesn't have any color/texture mapping.
I would guess either the textures either have not been copied to your hard drive or the textures director is corrupted. You might try this;
uninstall the existing program, restart and be sure you have no additional programs running other than what is running once you have first started your computer. Run the install again. Don't choose anything special. If there is an express installation, choose it. If it malfunctions again, follow the same procedure but choose advanced install and then choose all the options it offers. If that does not work, you may have a faulty disc. Give that a try.