[fw-db] Couldn't fetch mysqli

Hi,
I have this strange problem. If I try to use session save handler db
table - I get these errors:
<...>
Warning: mysqli::real_escape_string()
[function.mysqli-real-escape-string]: Couldn't fetch mysqli in
/var/www/blake.lt/library/library-1.7.0/Zend/Db/Adapter/Mysqli.php on
line 115

Warning: mysqli::prepare() [function.mysqli-prepare]: Couldn't fetch
mysqli in /var/www/blake.lt/library/library-1.7.0/Zend/Db/Statement/Mysqli.php
on line 77

Warning: Zend_Db_Statement_Mysqli::_prepare()
[function.Zend-Db-Statement-Mysqli--prepare]: Couldn't fetch mysqli in
/var/www/blake.lt/library/library-1.7.0/Zend/Db/Statement/Mysqli.php
on line 79

Warning: mysqli::real_escape_string()
[function.mysqli-real-escape-string]: Couldn't fetch mysqli in
/var/www/blake.lt/library/library-1.7.0/Zend/Db/Adapter/Mysqli.php on
line 115
<...>

So, I have initDb function, which initializes database:
$this->db = Zend_Db::factory(self::$_config->database->adapter,
self::$_config->database->toArray());
$this->db->query('SET NAMES utf8');
Zend_Db_Table::setDefaultAdapter($this->db);
And initSession:
Zend_Session::setOptions(self::$_config->session->namespace->toArray());
Zend_Session::setSaveHandler(new
Zend_Session_SaveHandler_DbTable(self::$_config->session->handler->toArray()));
$this->session = new Zend_Session_Namespace();

If I don't use dbtable savehander, then everything works fine - no
errors from the database.
And if I use dbtable savehandler - I get errors above.

Any suggestions?