Insert contour data into the drawing as AutoCAD polylines using the Insert to Drawing command.
In some situations, the surface keeps breakline or contour data (a list of their point coordinates), but does not associate them with an object. This may happen, for example, when you deleted an entity that the surface depends on, but the Copy Deleted Dependent Objects option on the Definition Tab of the Surface Properties dialog box is set to Yes. In this case, the surface simply converts its reference from a drawing entity to a list of points defining the object’s geometry.
To restore the reference to the object entity, you can insert the data associated with the deleted contour.