extending validation

[eluser]dimis[/eluser]
I make a

MY_Validation extends CI_Validation

at application/libraries and I make this function

Code:

function _check_setbox($val) {
       $CI =& get_instance();
        if ( $val !='-1') {
            return TRUE;
        }
        
         $CI->validation->set_message('_check_setbox', 'You must select a value.');
        return FALSE;
    }

Also at my code I write

Code:

$fields['collection']= "collection";
$rules['collection']    = "required|callback__check_setbox($collection)";

But it does not work, all other validation is ok but not this.
What is wrong?
Dimis