why cant i activate script with body velocity ?

s = script.Parent bvelocity = s.BodyVelocity a=script.Parent.Parent

if s.velocity > s.CFrame.lookVector * 10 then a.trail.enabled=true

end

i keep getting this error

17:18:22.159 - Workspace.bike.Model.Trail.Script:5: attempt to compare two userdata values

I am not too sure what you're trying to do, because you cannot compare vectors in such fashion. Please describe your situation.

But I will take a guess, that you want to compare distances. Then you'd do it this way:

s = script.Parent 
bvelocity = s.BodyVelocity
a=script.Parent.Parent

if s.velocity.magnitude > 10 then 
a.trail.Enabled=true
end