CakePHP redirect loop - cakephp

Question

I'm having the weirdest Cake error with my code. When the code below calls the add() method (also reproduced here and from a different controller), the code redirects him back with a 302 found HTTP code to the edit() action (in essence, to the user it appears as if nothing happens). To further complicate matters, when I call the same URL when I'm not on that page (despite the pages not being reliant on each other), I get redirected to the base of my app, which results in a redirect loop. I tried calling other methods from this controller (with their proper arguments) to see if this was just a problem with the add() action, but I get the same redirect loop. I've already checked all over SE but cannot find a relevant answer.
Here is the relevant code:
function edit($id=null) {
if(!$id) {
$this->Session->setFlash('Invalid!');
$this->redirect(array(
'action' => 'index')
);
}
else {
//Get the slides themselves
$slides = $this->Slide->find('all', array('conditions' => array('Slide.module_id' => $id)));
$this->set('slides', $slides);
//Get the data for the Module
$module = $this->Module->find('first',
array(
'conditions' => array (
'Module.id' => $id
),
'fields' => array(
'Module.module_name',
'Module.id')
)
);
}
}
And here is the add() code (again, from a different module):
function add($module = null) {
if ($this->request->is('get')) {
//Set some variables for the view (this code I know works as it has been used successfully elsewhere
}
else { //User is POSTing
$this->Slide->create();
$this->Slide->save($this->data);
}
}
Thanks to everyone in advance; I couldn't do this without your support!
EDIT: Here is the AppController code:
public $components = array(
'Auth' => array(
'authorize' => array(
'Actions' => array('actionPath' => 'controllers')
),
'loginAction' => array(
'controller' => 'users',
'action' => 'login'
),
'authenticate' => array(
'Form' => array(
'fields' => array('username' => 'email')
)
),
'logoutRedirect' => array('/')
),
'Session'
);
public $helpers = array('Html', 'Form', 'Session');
public function isAuthorized() {
return true;
}
public function Controller() {
}
}