Page overlay report may not work because of various reasons. I can list two of them from the top of my head:
- tracked page doesn't support https and Piwik was loaded via https (or even there's a force_ssl setting in the config)
The easiest solution here is to not force ssl and to run Piwik via http when one wants to see the Overlay report
- 'X-Frame-Options' are set to 'SAMEORIGIN'.
The solution here is to change the X-Frame-Options header
It would be nice to display a message informing users, why the Page Overlay report doesn't work. I think that it's a high-valuable and easy improvement.