Path Animation Evaluation Time keyframe error I've used Control + P ➔ Follow Path to animate an object along a path, and now I want to keyframe when the animation should start and end, but when I try to set a keyframe for the Evaluation Time value in the Curve Object Data panel, I get an error like in the screenshot.

What am I doing wrong? Or is there a different way of setting the start and end frame of the Follow Path animation?

Thanks for your help.
I guess you have automatically generated an animation and you need to delete if before creating any keyframe on the Evaluation Time value: 


Select your bezier curve.
Open the Graph Editor.
Unfold BezierCurve on the left to select the Evaluation Time track.
Press N to display the Graph Editor properties panel on the right.
Press the Modifiers tab.
Delete the Generator modifier.