Also the same error with the FSX TO PREPAR3D MIGRATION TOOL.
That migration tool is probably the cause of the problem, it must have left traces of it, even if disabled (if you tried it with the program disabled and enabled).
- Be sure NO "fake" FSX.EXE is present in the P3D folder
- Be sure the registry keys for P3D are pointing to the P3D folder, which is where they are supposed to point at in a correct installation
- Be sure the registry keys for FSX are pointing to the FSX folder, which is where they are supposed to point at in a correct installation
The registry key for P3D is located at HKEY_LOCAL_MACHINE\Software\LockheedMartin\Prepar3D\SetupPath
The registry key for FSX is located at HKEY_LOCAL_MACHINE\Software\Microsoft\Microsoft Games\Flight Simulator\10.0\SetupPath
Check both keys with REGEDIT and be sure they both point to the actual installed folders and, if you don't have FSX installed, remove the FSX registry key.