But alas, still nothing is happening, I just get the generic 500 error. Here is my code. I haven't changed anything out of the box with SWFUpload, except setting debug to true in swfupload/_config.php:

* swfupload/code/SWFUploadControls.php (as is, out of the box)

class SWFUploadControls extends Controller
{
	public static $image_class = "Image";
	public static $file_class = "File";
	
	public function handleswfupload()
	{
		if (isset($_FILES["swfupload_file"]) && is_uploaded_file($_FILES["swfupload_file"]["tmp_name"])) {
			$ext = strtolower(end(explode('.', $_FILES['swfupload_file']['name'])));
			$class = in_array($ext, array('jpg','jpeg','gif','png')) ? self::$image_class : self::$file_class;
			$file = new $class();
			$u = new Upload();
			$dir = SWFUploadConfig::get_var('default_upload_dir');
			if(!$dir) $dir = "Uploads";
			$u->loadIntoFile($_FILES['swfupload_file'], $file, $dir);
			$file->write();			
			echo $file->ID;
		} 
		else {
			echo ' '; // return something or SWFUpload won't fire uploadSuccess
		}
		
	}
}

* ssprojects/code/MessageForm.php (my custom form subclass)

class MessageForm extends Form
{
    function __construct($controller, $name, $id = 0)
    {
        SWFUploadConfig::addFileTypes(array(
            'pdf'
        ));
        
        $fields = singleton('Message')->getFrontEndFields();

        
        $fields->push(new HiddenField('ProjectId', 'ProjectId', $id));
        $fields->push(new SWFUploadField($name, 'Files', 'Upload Message Files', array('file_upload_limit' => '1')));

        $validators = new RequiredFields('Body');

        $actions = new FieldSet(new FormAction('submit', 'Save Message'));

        parent::__construct($controller, $name, $fields, $actions, $validators);
    }
}

* ssprojects/code/Project.php (my controller and the method that gets the form)

class Project_Controller extends Page_Controller
{
    function MessageForm($id = 0)
    {
        $params = $this->getURLParams();
        
        if ($params['ID']) {
            $id = (int)$params['ID'];
        }
        
        return new MessageForm($this, 'MessageForm', $id);


    }
}

As I understand it, this should at least save a file to the Uploads directory, correct?