You are importing data into a surface that already contains points. You may want to go back, create a new surface, and import the data into that instead. You can continue, and Revit will sew the meshes together, but the boundary may be larger than you want.

public static FailureDefinitionId SurfaceExists { get; }

Public Shared ReadOnly Property SurfaceExists As FailureDefinitionId
	Get

public:
static property FailureDefinitionId^ SurfaceExists {
	FailureDefinitionId^ get ();
}