json encode

[Gioiello]

Qualcuno sa quest'errore come posso risolverlo:

The character encoding of the HTML document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the page must to be declared in the document or in the transfer protocol.


return window.JSON.parse( data );

dove la mia chiamata ajax è

function get_messages (){
            //alert(base_url+ "index.php/chat/ajax_get_message/"+ chat_id);
            $.ajax({
                            type: "POST" ,
                            dataType: "json" ,
                            url: base_url + "index.php/chat/ajax_get_message/" + chat_id ,
                            success: function(data){
                                                    alert("1");
                                                    if (data.status == 'ok'){
                                                             $('#my_chat_view').html(data.content);
                                                             alert("2");
                                                    }
                                                    alert("3");
                                     }
            }); 
            return false;
        }
        get_messages(); 

e il mio controller

function ajax_get_message($chat_id){
        
        $messages = $this->chat_model->chat_get_messages($chat_id);
        $result = array('status'=>'ok','content'=> '');
        //header('Content-Type: application/x-json; charset=utf-8');        
                //return json_encode($result);
        if ($messages->num_rows() > 0){
            
            
            $messages_html = '<ul>';
            
            foreach ($messages-> result() as $mess){
                $messages_html .= '[*]'. $mess->message .'';
            }
                
            $messages_html .= '[/list]';
            
            $result = array('status'=>'ok','content'=>$messages_html);
            //header('Content-Type: application/x-json; charset=utf-8');
            return json_encode($result);
            
        } 
        else{
            //header('Content-Type: application/x-json; charset=utf-8');
            $result = array('status'=>'ok','content'=> '');
                
            return json_encode($result);
        } 

Ho provato a mettere i meta tag sopra l'header cosi

<meta content="text/html;charset=utf-8" http-equiv="Content-Type">
<meta content="utf-8" http-equiv="encoding">