During the demo site installation (while importing the demo content of the WordPress theme) you got the following messages (example):

167/167 Theme options loaded
161/161 Posts, pages, menu and media loaded
77/77 Widgets loaded
1/1 WP options loaded
Sorry, an error occurred. Please try to import again or use the standard WordPress Importer plugin.

What does it mean?

The import of theme options, posts, pages, menu, media, widgets, WordPress options and other elements except Revolution Slider went correctly. All you have to do is to import slider manually.

Solution:

Error while importing demo content is related to the new version of Revolution Slider plugin. Please follow this tutorial to import slider.