Why is this code erroring?

 cbcurp1=Vector3.new(cbcur1.X,cbcur1.Y,cbcur1.Z)
 cbprevp1=Vector3.new(cbprev1.X,cbprev1.Y,cbprev1.Z)
 cb1.CFrame=CFrame.new(cbcurp1:Lerp(cbprevp1,.5),cbprevp1)

Problem: The code sends the brick to a position of -395839927957385 or something similar.