There is a small problem while updating the slider on the website. I receive an error saying 'Empty ajax response!'. When I want to upload a picture on the slider this message shows up. What should I do?
In most cases when you have some ajax error in revolution slider means that rev slider have problem connecting to database. Maybe you have unstable internet connection and internet is down when you hit save button, or if there is some problem with server and request is not reaching the server - my bet is that the problem is something like that.
From the description of your error I can see that you are using older version of the revolution slider. So if this is the case try updating or installing new version and maybe they have solved the problem in the never versions (if internet is not the issue.) But remember to backup your slider before you do that.