BCE0019 errors in Custom Editor script

A quad is created from a menu item , then it can be edited in edit mode. However my Custom Editor cannot see the quad.

Assets/Editor/SQuadInspector.js(29,24): BCE0019: 'size' is not a member of 'UnityEngine.Object'. etc, etc ...

The editor script is the problem, the quad script is just a generic pocedural 4 vert mesh script.

My Editor script :

 #pragma strict
 
 // Add menu to the main menu
 @MenuItem ("Custom Item/Create Empty as SQuad")
 static function CreateGameObjectAsSQuad() 
 {
     var go : GameObject = new GameObject("GameObject");
     go.transform.name = "sQuad";
     go.transform.position = Vector3.zero;
     go.AddComponent("SQuad");
 }
 
 // ----
 
 @CustomEditor (SQuad)
 
 class SQuadInspector extends Editor 
 {
      // Using a SerializedProperty after the object has been deleted is not possible.
      // UnityEditor.DockArea:OnGUI()
  
     private var btnWidth : GUILayoutOption = GUILayout.MaxWidth(80.0);
     private var btnCenter = new GUIContent("Center", "Recenter quad");
  
         ///* // ----
     function OnInspectorGUI() 
     {
         EditorGUILayout.BeginHorizontal();
         target.size = EditorGUILayout.Vector2Field("Size", target.size);
         target.center = EditorGUILayout.Vector2Field("Handle", target.center);
         EditorGUILayout.EndHorizontal();
  
         if(GUILayout.Button(btnCenter, btnWidth)) 
         { 
             target.center = Vector2.one/2.0; 
             target.Construct(); 
         }
  
         EditorGUILayout.BeginHorizontal();
         target.uvSize = EditorGUILayout.Vector2Field("uvSize", target.uvSize);
         target.uvOffset = EditorGUILayout.Vector2Field("uvOffset", target.uvOffset);
         EditorGUILayout.EndHorizontal();
  
         if (GUI.changed) 
         {
             target.Construct();
         }
     }
         //*/ // ----
  
         ///* // ----
     function OnSceneGUI() 
     {
         if (GUI.changed)
         {
             EditorUtility.SetDirty (target);
         }
     }
         //*/ // ----
 }

My SQuad script :

remember this is just for reference to my editor script.

 #pragma strict
 @script RequireComponent(MeshFilter, MeshRenderer)
 
 // ----
 // instead of @script ExecuteInEditMode()
 @ContextMenu ("Do Something")
 function DoSomething () 
 {
     Debug.Log ("Perform operation");
  ConstructOnCreation();
     
 }
  
 function ConstructOnCreation() 
 {
  if(!mesh){
  GetComponent(MeshFilter).mesh = mesh = new Mesh();
  
  verts = new Vector3[4]; 
  uv = new Vector2[4];
  tris = new int[6];
  normals = new Vector3[4]; 
  mesh.name = "sQuad Mesh";
  }
  
  Construct();
 }
 // ----
 
 public class SQuad extends MonoBehaviour
 {
  public var size : Vector2 = Vector2.one;
  public var center : Vector2 = Vector2.one / 2.0;
  private var mesh : Mesh;
  private var uv : Vector2[];
  private var verts : Vector3[];
  private var tris : int[];
  private var normals : Vector3[];
  private var origVerts : Vector3[];
  public var uvSize : Vector2 = Vector2.one;
  public var uvOffset : Vector2 = Vector2.zero;
  
  function Start() 
  {
  if(!mesh){
  GetComponent(MeshFilter).mesh = mesh = new Mesh();
  
  verts = new Vector3[4]; 
  uv = new Vector2[4];
  tris = new int[6];
  normals = new Vector3[4]; 
  mesh.name = "sQuad Mesh";
  Construct();
  }
  }
  
  function Update () 
  {
  if (Input.GetMouseButtonUp(0)) Construct();
  }
  
  function Construct()
  {
  verts[0] = new Vector3( size.x * (0 - center.x), size.y * center.y, 0);
  verts[1] = new Vector3( size.x * (0 - center.x), -size.y * (1-center.y), 0);
  verts[2] = new Vector3( size.x * (1 - center.x), size.y * center.y, 0);
  verts[3] = new Vector3( size.x * (1 - center.x), -size.y * (1-center.y), 0);
  
  uv[0] = new Vector2(uvOffset.x, 1.0 - uvOffset.y);
  uv[1] = new Vector2(uvOffset.x, 1.0 - uvOffset.y - uvSize.y);
  uv[2] = new Vector2(uvOffset.x + uvSize.x, 1.0 - uvOffset.y);
  uv[3] = new Vector2(uvOffset.x + uvSize.x, 1.0 - uvOffset.y - uvSize.y);
  
  normals[0] = -Vector3.forward;
  normals[1] = -Vector3.forward;
  normals[2] = -Vector3.forward;
  normals[3] = -Vector3.forward;
  
  tris[0] = 0;
  tris[1] = 2;
  tris[2] = 1;
  tris[3] = 1;
  tris[4] = 2;
  tris[5] = 3;
  
  mesh.vertices = verts; 
  mesh.uv = uv;
  mesh.triangles = tris;
  mesh.normals = normals;
  
  mesh.RecalculateBounds();
  mesh.RecalculateNormals();
  }
 }