Motion Graphics Template from Live Text Template

I am try to save as a Motion Graphic Template in the new 2017.1. I am getting this error message, could someone explain what a property controller is.

here's the relevant help file for this new feature with a nice instructional video:

Create Motion Graphics templates with Essential Graphics panel

you link properties to property controllers in the essential graphics panel, then you can export them as motion graphic template. property controllers are the controllers that appear in the essential graphic panel once you drag the property from the timeline to the essential graphic panel.