[icsander]

Попробуй так:

Код:

procedure TForm2.btn3Click(Sender: TObject);
begin
  bt:=True;
  if (not Assigned(Form4)) then
     Application.CreateForm(TForm4, Form4);//  <-----
      Form4.Show;
end;

<if (bt=true) then> = <if bt then>
<exit;> - лишнее