[Codeigniter] Grafici con JPGraph

[fermat]

ho cambiato il model in questo modo:

<?php

class Report_model extends CI_Model {

    public function graphEntrate() {
        $this->db->select('causali.causale_nome AS Causali, SUM(entrata_valore) AS Valore');
        $this->db->from('entrate');
        $this->db->join('causali', 'entrate.causale_id = causali.causale_id');
        $this->db->group_by("Causali");
        $this->db->order_by('Valore', 'DESC');
        $this->db->limit(10);
        $query = $this->db->get();
        $arrResult = array();
        foreach ($query->result() as $var) {
            $arrResult[$var->Causali] = $var->Valore;
        }
        return $arrResult;
        //return array(1, 3, 6);
    }

}

adesso mi viene restituito un errore diverso:

A PHP Error was encountered

Severity: Notice

Message: Undefined offset: 0

Filename: jpgraph/jpgraph.php

Line Number: 5515
----------------------------
A PHP Error was encountered

Severity: Notice

Message: Undefined offset: 1

Filename: jpgraph/jpgraph.php

Line Number: 5515

ecc..........