Playing (4K) Video in Unreal


I am trying to make 4K video work in Unreal. I wanted to start small and just test out a video in Unreal using the tutorial at:

This works fine on one of my rigs, but when I try another one, I cannot get it to work. I get the following error message, every time I try to play the video in the Media Player in Unreal:

LogMediaUtils:Error: Cannot play file://XXX/sharks.mp4, because none of the enabled media player plug-ins support it:
LogMediaUtils:Error: | AndroidMedia (only available on Android, but not on Windows)
LogMediaUtils:Error: | AvfMedia (only available on iOS, Mac, but not on Windows)
LogMediaUtils:Error: | WmfMedia (URI scheme or file extension not supported)

I checked the codecs, and installed the latest from K-lite, to no avail. I cannot think of another reason why this does not work. Both rigs have the same version of Unreal (4.16.1).

Any idea what is going wrong here, and why I get these errors?