Глобальный хук клавиатуры для системных приложений. Почему зависает?

function KeyBoardHook(code:integer; wparam:wparam; lparam:lparam):Lresult; stdcall;
begin
  windows.beep(200,70);
  Result := CallNextHookEx(0,code,wParam,lparam); 
end;

library hdll;
 
{$mode objfpc}{$H+}
 
uses
  Classes,windows, unitCallback
  { you can add units after this };
 
var h:HHOOK; f:textfile; cb:TCallback;
 
  function hEvent(nCode:longInt;wPara,lPara:integer):LRESULT; stdcall;
  var d:PCWPRETSTRUCT;
  begin
    if (nCode>=0)and(wPara<>0) then begin
      if Assigned(cb) then cb(nCode,wPara,lPara);
    end;
   Result:=CallNextHookEx(h,nCode,wPara,lPara);
  end;
 
function Hook(acb:TCallback;hctype:LongInt):Cardinal;   export;
var hp:HOOKPROC;
begin
   cb:=acb;
  Result:=h;
end;
 
function Unhook:Boolean; export;
begin
 Result:=UnhookWindowsHookEx(h);
end;
 
exports Hook,Unhook;
begin
end.

unit Unit1;
 
{$mode objfpc}{$H+}
 
interface
 
uses    windows,  unitCallback,  msgs,
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls;
 
type
 
  { TForm1 }
 
  TForm1 = class(TForm)
                Memo1: TMemo;
        procedure Button1Click(Sender: TObject);
    procedure FormClose(Sender: TObject; var CloseAction: TCloseAction);
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
  public
 
    { public declarations }
  end;
 procedure callbackMe(nCode:longInt;wPara,lPara:integer);
 Function Hook(acb:TCallback;act:LongInt):Cardinal; external 'hdll.dll';
 function Unhook:Boolean; external 'hdll.dll';
 
var     st:TstringList;
  Form1: TForm1;
 
implementation
 
procedure callbackMe(nCode: longInt; wPara, lPara: integer);
var d:PCWPRETSTRUCT; c,t:array[1..100] of char;
begin
 d:=Pointer(lPara);
 FillChar(c,100,0);FillChar(t,100,0);
 GetClassName(d^.hwnd,@c[1],100);
 GetWindowText(d^.hwnd,@t[1],100);
 st.Append(format('hwnd=%20d  msg='+MessageToStr(d^.message)+'(%20x) lParam=%20d wParam=%20d ('+Trim(c)+') - ['+trim(t)+']'
  ,[d^.hwnd,d^.message,d^.lParam,d^.wParam]));
end;
 
{$R *.lfm}
 
{ TForm1 }
 
procedure TForm1.FormClose(Sender: TObject; var CloseAction: TCloseAction);
begin
  st.SaveToFile(ExtractFilePath(ParamStr(0))+'hook.txt');
  if Unhook then ShowMessage('Отцепились');
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
 
end;
 
procedure TForm1.FormCreate(Sender: TObject);
var h:Cardinal;
begin
  st:=TStringList.Create;
  h:=hook(@callbackMe,WH_CALLWNDPROC);
  if h=0 then RaiseLastOSError else Caption:=IntToStr(h);
end;
 
end.