请教delphi高手
有如下一段程序，运行时，在第一个窗口按按钮能打开第二个窗口，在第二个窗口按第一个按钮能打开第三个窗口，但在第二个窗口按第二个按钮不能打开第四个窗口，不知何解，望有高手能指出。
program Project1;

uses
Forms,
Unit1 in 'Unit1.pas' {Form1},
Unit2 in 'Unit2.pas' {Form2},
Unit3 in 'Unit3.pas' {Form3},
Unit4 in 'Unit4.pas' {Form4};

{$R *.res}

begin
Application.Initialize;
Application.CreateForm(TForm1, Form1);
Application.Run;
end.

//第一单元

unit Unit1;

interface

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

type
TForm1 = class(TForm)
Button1: TButton;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation
uses unit2;
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
form2 : TForm2;
begin
form2 := TForm2.Create(self);
form2.ShowModal;
form2.free;


end;

end.


//第二单元

unit Unit2;

interface

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

type
TForm2 = class(TForm)
Button1: TButton;
Label2: TLabel;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form2: TForm2;

implementation
uses unit3, unit4;
{$R *.dfm}

procedure TForm2.Button1Click(Sender: TObject);
var
form3 : TForm3;
begin
form3 := TForm3.Create(self);
form3.ShowModal;
form3.free;
end;

procedure TForm2.Button2Click(Sender: TObject);
var
form4 : TForm4;
begin
form4 := TForm4.Create(self);
form4.ShowModal;
form4.free;
end;

end.


//第三单元


unit Unit3;

interface

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

type
TForm3 = class(TForm)
Label1: TLabel;
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form3: TForm3;

implementation

{$R *.dfm}

end.


//第四单元

unit Unit4;

interface

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

type
TForm4 = class(TForm)
Label1: TLabel;
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form4: TForm4;

implementation

{$R *.dfm}

end.

[解决办法]
没有问题,不过这些定义都可以省去
var
form2 : TForm2;
form3 : TForm3;
form4 : TForm4;


[解决办法]
你的第二个按钮没有关联事件到Button2Click吧？