I've just spent the last hour or so banging my head against a brick wall trying to figure out why I'm unable to retrieve some data via AJAX even though I know data is being returned as I can see it in my error log.

Turns out the permission system I wrote a few days ago actually works and because I didn't specify a permission it automatically denied my user from retrieving the data. One thing I forgot to add was an error message to tell me when I don't have sufficient permission to do something. Adding a message could have just saved me a lot of time :/