PHP4: Call to a member function on a non-object

[eluser]Unknown[/eluser]
On PHP5 it works fine.

The model:

Code:

<?php
class Selecty_model extends Model {

    function Selecty_model()
        {
            parent::Model();
        }

    function isVyrobce($vyrobce){
            $CI =& get_instance();
....
....
....

I really don't know... :-(