The root is D:\ not D:\Prepar3D V4 or any other name.
Installing any software in the root of a drive, it's always a bad idea, because the root has some special protection from the OS to prevent users from mistakenly destroying a whole drive, so installers will usually have problems setting the correct permissions, which are required for the software to work.
Older version of our installers explicitly prevented to install into the root of the drive and, since this is known to be a bad practice, by default it's disabled in the kit we use to create installers (Inno setup), but since some users complained about this, we removed this restriction.
I suggest to uninstall everything, and reinstall into D:\Prepar3d v4