Attach actor to path, not satisfied

Hello again, I'm trying to attach an actor to a path for a 3D animation project. I've got a bulldozer that needs to follow a path where the dozer stays perpendicular to the path as it bends and then straightens back out. I've created the actor for the dozer, with the origin where the path touches the tread, but when I try to define the path I get a "relationship not satisfied" message. The direction of the path element is correct. What am I missing here? I've tried to search the forum for an answer, but didn't find what I needed, and the Microstation help file wasn't helpful at all. Here is a screenshot of the dozer & path:

Thanks for your help,

Kevin

MS 08.11.09.829 SS4 Win 10 Pro