This is a common error message right after the dummy data import. It is the slider added in the demo data, the one your page is asking for and not finding. But being Revolution slider a third party plugin which you need to install independently from the theme, this “home” slider, also needs to be installed first.

You can create a new slider and then select it in the page’s options > Slider Options. Or import existing ones from Revolution Slider > Import Slider. Find the demo slider’s zip files in the “sliders-dummy-data” folder. This folder is inside the main theme zip file, that you first downloaded from Envato.