After selecting object, cursor changes to circle with a slash

In a file that I’ve previously worked on with no problems, after making a selection and moving my pen to the object to transform or adjust the contour, I get a grey circle with a slash through it and can’t do anything. What happened that I can select an object, but not manipulate it? I must have accidentally changed a pref someplace. It’s NOT a Line art VS color art layering issue.

BUT, if I switch to drawing mode, the tools work fine. But I need the rest of my drawing for reference. Ideas?