'System Error. Code: 1400. Недопустимый дескриптор окна'

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs,syncobjs, contnrs, StdCtrls;

type
  TMyThread=class(tthread)
  private
    FTime: integer;
  procedure ThreadTerminated(sender:tobject);
    procedure SetTime(const Value: integer);
  protected
  procedure execute;override;
  public
  property Time:integer read FTime write SetTime;
  constructor create;
  destructor destroy; override;
  end;


type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  threadlist:tthreadlist;

implementation

{$R *.dfm}

function ThreadsCount:integer;
begin
  result:=threadlist.locklist.Count;
  threadlist.UnlockList;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  threadlist:=tthreadlist.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  while ThreadsCount >0 do
  application.ProcessMessages;
  threadlist.Free;
end;

{ TMyThread }

constructor TMyThread.create;
begin
  inherited create(true); // создаем ожидающий поток, чтобы можно было изменять параметры
  FreeOnTerminate:=true;
  Priority:=tpNormal;
  OnTerminate:=ThreadTerminated;
  ThreadList.Add(self);
end;

destructor TMyThread.destroy;
begin
  threadlist.LockList;

  /// здесь может быть код, для освобождения объектов


  inherited;
  threadlist.Remove(self);
  threadlist.UnlockList;
end;

procedure TMyThread.execute;
begin
  // код, который должен выполняться в потоке.
  sleep(FTime);

end;

procedure TMyThread.SetTime(const Value: integer);
begin
  FTime := Value;
end;

procedure TMyThread.ThreadTerminated(sender: tobject);
begin
  showmessage('Поток завершил работу');
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i:integer;
  thread:tmythread;
begin
  for i:=1 to 10 do
  begin
    thread:=tmythread.create;
    thread.Time:=4000;
    thread.Resume;
  end;
end;

end.