I was editing a group ( door opening) and suddenly this message was in my model.
Could you explain it more? Is this a pop-up message? Or a tooltip next to the mouse cursor? Are you sure that this is the exact “message” and not something like “On Face in…” or “On Face Outside Active”. Can you take a screenshot of it?
If you are trying to measure, draw, or move, SketchUp is letting you know that the point you are interacting with lies exactly along the flat surface of an object rather than floating in space.