Asset warp tool will not add points

I created a parented set of symbols in Animate and now wanted to use the asset warp tool to animate them.  When I select any of the symbols in the project and try to use the Asset Warp Tool, it changes the pointer to an arrow with the circle and a line through it and will not allow me to create any points.  I am able to import some of the same png files into a different animation and parent them to other things and then can add points to them, but cannot do it to any assets in the one project.

I cannot find any documentation that explains what some causes for having this cursor might be.