"X is not a valid member" error, but X is present?

My script is a basic clickdetector script that works fine. It is meant to change the bodyvelocity in a part called "engine". The problem is that said bodyvelocity is not a valid member of engine, apparently.

I have tried renaming it and putting that name into the script, but nothing works. Does anybody know what the problem would be?

BodyVelocity.Velocity.X