I see my GET request for show_ads.js is failing. So perhaps that nonloading javascript is suppose to make it appear but it's non working at the moment... Now, which excuses from the site would apply here?
Here's the first one that might make sense that showed up on my refresh: "It worked yesterday"
UPDATE: Must be Ad Block blocking it.
Are you using Adblock or similar software?
Yup, it was Ad Block.
I'm not sure its hidden on purpose. There doesn't appear to be any styling to hide it, and when I went to the URL that the inner iframe was linking to (the iframe inside of the iframe), it gave a blank page.
I think Google banned the domain from Adsense. I had a neglected UGC site that gradually became inundated with shady links and content, and this happened to me. Perhaps a site with low clicks and repeated, short-lived ad serves is worth banning.
Sounds like something the advertisers wouldn't be very happy about...
The "click me as often as you can" contents for sure generate a lot of clicks. genius!