Hi Umberto,
I finally managed to get KJFK V1 to run in FSX.
One reason was that my Kaspersky AV was blocking the program from installing and running. I had to confirm that the program was a trusted software.
I then had to download GSX level 2 and activate it. GSX then required me to download the Standalone Manager again.
After I did all of that and including them in the Kaspersky Safe-list, KJFK V1 was up and running once again.
I had no idea that Windows 10 was so picky, almost every software that I download and try to install is seen as malicious.
Thank you for your patience and assistance.