My apologies for not responding sooner, folks. I was working on getting to the bottom of this. There was a change that was rolled out sooner than expected. We are in the process of rolling it back, and you should see this error stop within the next couple of hours. In the process of investigating this I found out there will be some minor changes happening with HTML5 template ads in the future, so please be on the lookout on
our blog for any upcoming changes. You can also subscribe to
AdWords API Announcements, which gets our blog posts as well.