I think the poblem lies in the fact that you installed Prepar3D v4 in C:\Program Files X86\etc..., when it would have been better to install it directly to the C: drive, in either C:\Lockheed Martin\Prepar3D v4, or C:\Prepar3D v4.

If you have a second HDD/partition (D: drive), it is even better than installing on the C: drive. As much as it is a pain in the neck, it might be better if you uninstall the 757 Captain III, then uninstall Prepar3D v4, and reinstall it in the loacations I suggested above. Do that, and everything should be okay.

I strongly recommend you to install both Prepar3D v4, and the 757 Captain III, using the "Run as administrator" option (right click on the installers and select "Run as administrator" from the list that pops up)!

Note. In Windows Vista, Windows 7, Windows 8/8.1, and Windows 10, you have restricted access to the C:\Program Files folder, and C:\Program Files x86 folder, so it is always better to install games elsewhere. This is even more restrictive in the Home Editions of those operating systems.