This error occurs when we try to drag and drop the exported index.html(of a HTML 5 Publication created from QuarkXPress) into a browser or directly click on this file to open it.

Solution:

Please either use the preview button (at the lower left hand corner of your document window) or deploy the exported files to a Web Server first, and then open index.html in a browser.
The reason for that is that some JavaScript need to be running, so you need to put it into a Web Server to display correctly.
You can use the default built-in Web Server on OS X or Windows machine. Or simply use the preview button, as it starts a local Web Server.

Image showing Preview Button in QuarkXPress: