new table for a new extension

I'm developing a new extension.
In this extension I add some fields to existing tables and 2 new tables.
When I upgrade the database, it tells me that the 2 new tables do not exist and try to recreate.

This is the code:

Code:

---

--
-- Table `tl_news`
--

CREATE TABLE `tw_message` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `pid` int(10) unsigned NOT NULL default '0',
  `tstamp` int(10) unsigned NOT NULL default '0',
  `title` varchar(255) NOT NULL default '',
  `alias` varbinary(128) NOT NULL default '',
  `author` int(10) unsigned NOT NULL default '0',
  `date` int(10) unsigned NOT NULL default '0',
  `time` int(10) unsigned NOT NULL default '0',
  `text` mediumtext NULL,
  `published` char(1) NOT NULL default '',
  `start` varchar(10) NOT NULL default '',
  `stop` varchar(10) NOT NULL default '',
  PRIMARY KEY  (`id`),
  KEY `pid` (`pid`),
  KEY `alias` (`alias`)
) ENGINE=MyISAM default CHARSET=utf8;


-- --------------------------------------------------------

--
-- Table `tl_news_archive`
--

CREATE TABLE `tw_message_archive` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `tstamp` int(10) unsigned NOT NULL default '0',
  `title` varchar(255) NOT NULL default '',
  `member_group` blob NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

---

Try DEFAULT instead of default in tw_message.