I don’t really know if it is possible that someone who has no admin access to an Invision Powered Forums can post his adsense ads on that forums.

It was actually reported on the Webmasters World that such site published the adsense which is not of the forums owner:

A coworker called and said that there was an error coming up on one of our sites. It is a message board. In I.E., there is a message “You are not authorized to view this page” in the middle of the page. The rest of the site works, but on the home page, this message appears. I checked the source and where that message appears is the script for adsense, at least I’m pretty sure it is anyhow.

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