{$I-}
 Append(f);
{$I+}
if IOresult <> 0 then ...

procedure AppendLog(const aFileName : string; const aData : string);
var
  f : TextFile ;
begin   
   AssignFile(f, aFileName);
   try
     if not FileExists(aFileName)  then 
        Rewrite(f) 
      else 
        begin
               Reset(f) ;
               Append(f) ;
        end ;

     Write(f, aData) ;
   finally
     CloseFile(f) ;
   end ;
end ;

procedure TForm1.Timer1Timer(Sender: TObject);
var
  fwNew, ActiveWindow: HWND;
  f, fil: TextFile;
  FileDir, Result, resultfin, resultpath, filedesc: String;
  Path: array [0 .. MAX_PATH] of Char;
  today, totime: TDateTime;
  pProcID: ^DWORD;
  procid: cardinal;
begin
  Try
    ActiveWindow := GetForegroundWindow;

    if GetWindowTitle(ActiveWindow) <> ttl then

    begin

      fw := GetForegroundWindow;
      if ShGetSpecialFolderPath(Application.Handle, Path, CSIDL_APPDATA, False)
      then
        if not DirectoryExists(Path + '\winactivitybeat') then
          if not CreateDir(Path + '\winactivitybeat') then
            raise Exception.Create('Ошибка создания каталога');

      FileDir := Path + '\winactivitybeat' + '\log.txt';

      today := Date;
      totime := Time;
      Result := getprocimagename(TakeProcessID(GetWindowTitle(ActiveWindow)));
      resultpath := Getpathfrompid(TakeProcessID(GetWindowTitle(ActiveWindow)));
      label2.Caption := Result;
      memo1.Lines.Clear;
      memo1.Lines.Add(GetExeVersionData(resultpath).FileDescription);
      filedesc := memo1.Lines.Text;

      { пишем в лог }
      AppendLog(FileDir, DateToStr(today) + ' ' + TimeToStr(totime) + '   ' +
        label2.Caption + '    ' + GetWindowTitle(fw) + '       ' + filedesc);

      ttl := GetWindowTitle(fw);
      Label1.Caption := 'Пишем в ' + FileDir;
      Form1.ClientWidth := Label1.ClientWidth + 15;
    end;
  except
    on E: Exception do
      if Label5.Caption <> E.Message then
      begin
        { пишем в лог }
        AppendLog(FileDir, DateToStr(today) + ' ' + TimeToStr(totime) + '   ' +
          label2.Caption + '    ' + E.Message + '     ' + Message1);

        Label5.Caption := E.Message;
      end
  end;
end;