I have 4 downloads of it of current downloading
If you see that error, it means you don't have the current version. Perhaps your browser is playing tricks on you by caching, so you are still getting the old installer over and over.
Try to clear your browser cache and download it again. To be absolutely sure of your download, check the date of the Digital Signature on the installer file Properties. The timestamp should be May 12th.
Its the same download that allows a full install into P3D but doesnt go into FSX.
There's no such thing as a download that allows P3D but doesn't allow FSX. If P3D is detected, you are offer the choice to install it there, but if you say NO, it will automatically go into FSX, without asking, by clearly indicating that is going to install into FSX BECAUSE you said NO to P3D.
If it doesn't go into FSX, it's because your FSX registry keys might be missing or pointing to the wrong folder. This is possibly caused by the P3D Migration Tool, which should be ALWAYS disabled when using proper P3D installers like our own, because it modifies the FSX registry to point to P3D.