What does "the selected layer does not have a motion path" mean?
That message is displayed when the "Motion Path Tool" is enabled and the selected layer does not have any layer motion to be shown. When the selected layer does have motion, the "Smoothness" tool is displayed in that location instead.
The "Motion Path Tool" can be toggled on / off from the controls shown just below the "Preview" area, near the slide number label. Look for the right-most icon in that list of controls, which has four dots connected by three lines in a zig-zag pattern.