1) There is one or more reference to a file or location that is non-secure. 2) Live Chat software JavaScript on your page that is referencing the chat site at a non-secure location.
To determine where the problem is, click "No" when you get this prompt and you will see the broken files on the page. To fix this you will need to fix the source code.
Go to the Site HTML editor of the section that contains the non secure file and you will see code that looks like this: src=http://www.domain.com/directory/filename OR src="/images/daytime.gif"
If the file that is referenced does reside at your domain then you will want to change the code to this: src="images/daytime.gif"
Note: Remove the / before the folder name
If the file does not reside on your site then you will want to obtain the file and upload it to a location on your site using the File Manager in your admin panel so that you can reference it within your site. After you have done this you will need to update the HTML accordingly.
If you are using a live chat application on your site you will need to contact that vendor to obtain the secure location of their code so that you can update the HTML reference to a secure location. If your live chat vendor does not offer their code at a secure location then there is no solution to this issue.