Have trouble in timeline

when I move the actor to new location, I use timeline and lerp(vector) to make it smoothly。But when I edit the float track in timeline edit,the line alway be gray,not red。
this is the tutorial I have following : https://answers.unrealengine.com/questions/144402/moving-actor-from-one-point-to-another-smoothly.html

Can you post a screenshot?
Did you add a float track?