Same problem here - a DirectRT item won't run via MediaLab.
MediaLab and DirectRT run fine on their own, including the particular experiments in question.
However, when trying to embed the DirectRT material into the MediaLab experiement, MediaLab stops at the point where DirectRT should kick off. And stays there. Forever. No warning messages, nothing. I need the task manager to close Medialab then. the computer doesn't crash though.
Next door, similar setup machine, the above experiment runs just fine!...(can't swap the computers though).