The more and more I think about this, maybe there was an update on windows which affected the extractor to corrupt the files.
A Windows update you are the only one that use it ?
I still do not think this on my system. The developers owe at least an explanation of how these files fit in the framework of the system and how this error could go wrong in any computer.
Of course it's your system, otherwise we would have been flooded by hundreds or even thousands similar reports, if the file were *really* corrupted, or a Windows update were somewhat not compatible with our installer. Instead, you are still the one and only reporting this specific problem so yes, it IS your system, no question about it.
And, you said yourself you had a similar problem with FS2Crew, which required to get the files in a different way so, clearly, something in your system is preventing you to get uncorrupted downloads, even when they are entirely unrelated to FSDT.
These are the files which are online now:
FSX
f594ad3ebec1e7a8eb4b301f8f7407dd gsx_fsx_setup.exe
23750eb455159a90aabc184cbce4c7f3 gsx_fsx_setup2.exe
3410a961476c765e75812ae9f73292df gsx_fsx_setup2-1.bin
b1a44dd431f01a25bab09319fac581d0 gsx_fsx_setup2-2.bin
1874c7b892a7caba01740112caab5f2b gsx_fsx_setup2-3.bin
P3D4
4efa30442652bd6537101078edec59eb gsx_p3d4_setup.exe
f184a84d887283f99e71fe055ca45524 gsx_p3d4_setup2.exe
20bd7390f65599824f41d78942c4673f gsx_p3d4_setup2-1.bin
4a3ce42de7e4088ef3ccb3107d739970 gsx_p3d4_setup2-2.bin
ab44002a4351642ca0d53674328e56f2 gsx_p3d4_setup2-3.bin
be9af183fdafc15ac8810b923b221a8b gsx_p3d4_setup2-4.bin
The first code is the MD5 hash. You can use this utility here.
http://www.winmd5.com/To verify the hash file for the files you downloaded.
If ALL hashes are matching, it means the download went fine, and something in your system is preventing to uncompress the files.
If one of the hashes doesn't match, it means something went wrong during the download.