quickreport释放出错问题待高手解决 (200分)

程序如下
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
Button3: TButton;
Panel1: TPanel;
procedure closeallform;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;
implementation
uses unit2,unit3;
{$R *.dfm}
procedure TForm1.closeallform;
begin
if Assigned(Form2) then
begin
form2.Close;
Form2.Free;
form2 := nil;
end;

if Assigned(Form3) then
begin
form3.Close;
Form3.Free;
form3 := nil;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
closeallform;
if not Assigned(form2) then
begin
Form2 := TForm2.Create(Application);
form2.Parent:=panel1;
form2.Show;
form2.Align:=alclient;
end;
// form2.ShowModal;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
closeallform;
if not Assigned(form3) then
begin
Form3 := TForm3.Create(Application);
form3.Parent:=panel1;
form3.Show;
form3.Align:=alclient;
end;
end;
end.

以上是主窗口代码，大意是把FORM2、FORM3显示在主窗口的PANEL1上，每次打开一个FORM前检查PANEL1上有无FORM打开，有则关闭。
FORM3上有一QRPREVIEW1，用来实现报表的自定义预览。
FORM3的大致代码：
unit Unit3;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, QRPrntr, ExtCtrls, DB, ADODB;
type
TForm3 = class(TForm)
Panel1: TPanel;
Button1: TButton;
Button2: TButton;
Button3: TButton;
Button4: TButton;
Button5: TButton;
Button6: TButton;
Button7: TButton;
Button8: TButton;
Button9: TButton;
ADOTable1: TADOTable;
QRPreview1: TQRPreview;
procedure Button8Click(Sender: TObject);
procedure Button9Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form3: TForm3;
implementation
uses unit4;
{$R *.dfm}
procedure TForm3.Button8Click(Sender: TObject);
begin
adotable1.Close;
close;
end;

procedure TForm3.Button9Click(Sender: TObject);
begin
adotable1.Open;
quickreport4.Preview;
end;

procedure TForm3.Button3Click(Sender: TObject);
begin
qrpreview1.Zoom:=100;
end;

end.

quickreport4中的 ONpreview 事件代码：
procedure TQuickReport4.QuickRepPreview(Sender: TObject);
begin
form3.QRPreview1.QRPrinter :=quickreport4.QRPrinter;
end;

整个过程是这样的，主窗口BUTTON2调用FORM3，在FORM1的PANEL1上能正常显示FORM3，
FORM3中TForm3.Button9Click也能在FORM3的QRPREVIEW1上正常预览报表，
问题出在如果我退出FORM3后再调用FORM1的CLOSEALLFORM就会提示出错。
错误提示是：
“Project Project1.exe raised exception class EAccessViolation with message 'Access violation at address 00403988 in module 'PROJECT1.EXE'. Read of address 00C7C000'. Process stopped. Use Step or Run to continue.”
查了下程序，问题出在CLOSEALLFORM中的：
if Assigned(Form3) then
begin
form3.Close;
Form3.Free;
form3 := nil;
end;
也就是说在释放FORM3时程序会出错，
搞不懂是怎么会事？是不是因为这时候QUICKREPORT还没释放？
如果在FORM3中没有对QUICKREPORT调用则不会出现这样的问题。
另，在PROJECT OPTION中FORM2、FORM3都不是自动创建的。

谁能给我一个回答？

在formclose事件中加上
action := cafree;

试过了，没用，只要FORM3一释放就会有错误出现。

不用试，QR做自定义报表释放时是有很多问题，一个办法是使用PreviewModal，但据QR帮助，最好用于基于线程的数据库

用PREVIEWMODAL也无济于事，一样会出现同样的问题。

用Previewmodal,去掉form3.free及form3:=nil,模式窗体让它关闭后自动释放.
在onClose中加入acTion:=cafree;

试试这样
if Assigned(Form3) then
begin
form3.Close;
end;
...
procedure TForm3.formclose(Sender: TObject;var Action: TCloseAction);
begin
action:=cafree;
form3:=nil;
end;