If you have never had HTTPS on your site, you will undoubtedly run into an issue with how your site assets are loaded. By assets I’m referring to things like images, JavaScript, and even your CSS; by default, they are often configured to load over HTTP. Insecure assets will not stop the padlock from showing in browsers, but it will add an exclamation point warning to your users that information is being loaded insecurely.

This can happen when the absolute URL path is set, instead of relative paths for images, CSS, or JavaScript files, or remote assets.

Absolute path:

<img src="http://mydomain.com/myimage.png">

Relative path:

<img src="/myimage.png">

If you view the source code of the web page giving you the error and search for "http://".  If you find any of this code it should be replaced with the "Relative Path" as described above.  This error is unrelated to any server related issues and is a result of coding that is not compatible with SSL use.