Hello luzzati,
I was experiencing exactly the same problem. Updated to the latest versions of the Avada theme (v. 3.9.2) and the problem was solved.
Hope this solves your problem as well.
Best regards,
kaduuken
Another possible fix:
http://www.agentwp.com/fix-cheatin-uh-error-in-wordpress/comment-page-1#comment-4575
Second fix mentioned worked for me, hope it helps.
PS.: updating your theme with a fix from the theme creator is still the best option
