Can't load session library

[eluser]can35[/eluser]
Hi
I'm trying to load Session library in my site but I get the following error:

Fatal error: Call to undefined method CI_DB_mysql_driver::where() in /MY_PATH/system/libraries/Session.php on line 201

If I use: $this->load->library('session');
or try with the autoload feature, I get the same message.

What can I do?

Thanks in advance