Thanks for writing in.
There are no other rules except that you will activate the plugin cornerstone and other extensions of X that needed in your demo content like Revolution Slider.
You can check the link below for more details regarding demo content.
If still not helping, please try to reinstall your X theme and Cornerstone then do not add other plugins yet before setting up again demo content. Don't forget to clear your cache for demo content. Check the link above in troubleshooting on how to do it.
Let us know how it goes.