The script in the docs page assumes that Ornatrix wasn't installed and loaded when you open the scene, so all Ornatrix nodes appear as "unknown".

In your case you have installed the demo version, so once you load the scene you should manually delete all objects of type HairShape from the scene. And also run that 'OxInstallRenderCallbacks( 0 )' MEL command.

I suppose you could modify that script to remove HairShape (or any other types of) objects automatically by replacing "unknown" in the type parameter with "HairShape". But maybe it's better to do it manually.