403 Forbidden Error in Ajax call Actually this is first time to implement Ajax in drupal.
I would like to implement a user name validation using Ajax in user register section. When a user enter his name and filling another field, then validation is  running and if the user name already existing in the system, then a error message  shows, the user name is already taken.  I used to call the Validation function on "blur" event of Jquery.  The Jquery cod is below

$("#edit-name").blur(function()
{
$.post(Drupal.settings.basePath + "username_checking",{user_name:$(this).val()} ,function(data)
    {
if(data=='no') //if username not avaiable
      {
        $("#msgbox").fadeTo(200,0.1,function() //start fading the messagebox
        { 
          //add message and change the class of the box and start fading
           $(this).removeClass();
          $(this).addClass('messageboxerror');
          $(this).html('&lt;img align="absmiddle" src="images/Error.png" /&gt; Username Not Available...').show().fadeTo(1900,1);
          disable();
        });     
      }
 }              
    });
 }
});


and I implemented the function in a hook menu as below,

    $items['username_checking'] = array(
'title' =&gt; 'username_availability',
'page callback' =&gt; 'username_availability',
'access arguments' =&gt; array('access caubo_registration content'),
'type' =&gt; MENU_CALLBACK
);


and function is here

function username_availability() {
$user_name = $_POST['user_name'];
$select = "SELECT name FROM name WHERE user_name='%s' LIMIT '%d'";
$result = db_query($select,$user_name,1);   
$node = db_fetch_object($result);
if($node-&gt;name = $user_name){
  return "yes";
}
else{
  return "no";
}
}


It shows the error in Firebud 
POST http://localhost/WC/drupal_website/username_checking
403 Forbidden

I want to confirm is my method is right or not ? If right please solve the problem, or give the exact way to do.
if this is a registration function for anonymous users do they have the respective access caubo_registration content permission set in User Permissions?