JQuery :: Form Plugin AJAX File Upload?

I am trying to implement this jQuery form plugin to do ajax file uploads. Although the documentation is great I am still a little unclear about one thing. Usually when I do ajax submissions I return a response in JSON(using PHP), something like :

<?php
echo json_encode(array("status_message"=>"success"));
?>

When doing some simple tests I have run into a problem and I believe it is due to the way this plugin handles JSON responses. My form :

[Code]...

This does not result in the success event firing but rather the error event. In the plugin documentation it states that it does not handle json responses well and that it recommends wrapping the response in a textarea. Unfortunatly I'm not sure what they mean by that, and what I've tried so far has not worked. ould anyone give me some advice as to how to output the response in JSON properly? Could anyone that has used this plugin for AJAX file uploads offer any advice on doing so?