Selur's Little Message Board

No clue what is up with your system. Works fine here on Win10.
Wild guess is that you got something else installed that is causing issues.

Managed to reproduce the problem,...

Uploaded a new dev which should fix the problem.

Cu Selur

Many thanks kind sir, will check it out tomorrow.

When I click preview, I see this:

Try an older version from: https://github.com/dubhater/vapoursynth-.../releases/
My guess is the newer mvtools version requires some cpu support which your cpu doesn't support.