I'm having this issue too. I as well have cleared the cache. Had to reload dreamweaver and applied the update and it turned off the extensions. Used the dmx extension to install all (which seemed like the quickest way to turn them back on). I just tried reapplying the extension and clearing the cache before running dreamweaver again, ran it, applied the serial number, closed it, reran it and still got this error.
Nope that didn't fix it. It's on the first attempt to save after just opening dreamweaver and make a change, then save it, that dialog box pops up. Then I don't see it again until the next time I open dreamweaver and attempt the first save again.
uninstalled, cleared cache, done all the steps in order three times and Advance HTML Editor 3 does not work. This is the first DMX extension where I haven't been able to resolve the issue. This is CS6. Very frustrated. About to request a refund for this extension.
I discovered that the sliding billboard extension was in conflict with a Yahoo merchant extension I had installed. I removed the Yahoo extension cleared the cache reinstalled the sliding billboard extension and now everything is working as it should.