Probleme mit Create eigener klasse -> Zugriffsverletzung

[Super_Chemiker]

Delphi-Quellcode:

unit Jong;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, stdctrls;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);

  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

  TStein = class(TGraphicControl)
  private
    { Private-Deklarationen }
    x,y: Integer;
    Color: TColor;
    Pressed: Boolean;
  protected
    { Protected-Deklarationen }
    procedure Paint; override;
    procedure MouseDown
      (Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
  public
    { Public-Deklarationen }  
    constructor Create(AOwner: TComponent); override;
    property Caption;
  end;  

var
  Form1: TForm1;
  test: TStein;
  
implementation

{$R *.DFM}

constructor TStein.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  Color := clBtnFace;
  Canvas.Brush.Color := Color;
  Pressed := false;
  Caption := 'Test';
  SetBounds (0,0,50,50);  
end;                     

procedure TStein.MouseDown (Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  inherited MouseDown (Button, Shift, X, Y);
  if Button = mbLeft then
  begin
    Pressed := true;
    Paint;
  end;
end;

procedure TStein.Paint;
begin
  x := (Width - Canvas.TextWidth(Caption)) div 2;
  y := (Height- Canvas.TextHeight(Caption)) div 2;
  Canvas.Rectangle (3, 3, Width-3, Height-3);
  canvas.TextOut(x,y, Caption);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  test := TStein.Create(self);
end;

end.

bitte sehr!