403 error in AJAX to Controller

You need to provide a lot more information than just this, before anyone can help you.
The only thing someone could point out is that a 403 is "access forbidden", if that helps.

View->textbox.php

Code:

<div style="text-align:center;">
    <input id="txt_short" type="text"/>
    <input id="btn_short" type="submit" value="Go" />
    <p id="show"></p>
</div>
<script>
                $(document).ready(function(){
                $("#btn_short").click(function(){
                var l =$("#txt_short").val();
                $.ajax({type:"POST",url:"../../App/Controllers/Links.php",data:"?l="+l,done:function(msg){
                    $("#show").html(data);
                        }});
                     });
                 });
</script>

Controller->Links.php

PHP Code:

class Links extends Controller
{
        public function index()
        {
                helper('html');
                helper('form');
                $p= $_POST["li"];
        }
}