$this->db->select_max('field') - not working?!?!

[eluser]einstein[/eluser]
Hi.
So according to this page:
http://ellislab.com/codeigniter/user-gui...ecord.html,
I should be able to do this:
$this->db->selectmax('user_id');
$query = $this->db->get("tblusers");
(this code is from my model)
But i get this error:
Call to undefined function: select_max()
Active record is not turned off. I tryed also selectmax() but no luck,
Any suggestions?
Thank you