Chaining CodeIgniter model method to $this->db object fails with "Call to undefined method CI_DB_mysql_driver::methodName()" [closed]

When I try to call one of my model methods, I am getting this error:

Fatal error: Call to undefined method CI_DB_mysql_driver::findVenueInfo()

The method called is from my controller:

function searchVenue()
{
    $this->load->model('venues');
    //get venue info
    $data['info'] = $this->db->findVenueInfo($this->uri->segment(3)); //this line generates the error
}

and the findVenueInfo() method is in the model (venues.php).