It shouldn't be a popup, that's for sure, but it does look like it's originating from the small banner ad at the top of the page.

1. Does a new page popup with this error, or does the error load within the page you're on?

2. Are you getting this on every thread page on FlyerTalk, or only in certain areas (if so, can you tell me which ones)?

3. Does this happen as soon as you come to FlyerTalk's main page (http://www.flyertalk.com)?

I think that ad code ("http://ad-adex3.flycast.com/...") is from our old ad company, and shouldn't still be on our sites... I'll verify that, though.

In the meantime, could you try clearing out your browser's cache to see if that helps any?