1. Though your website is a SSL protected website, when all the contents in your web page are not fully secure HTTPS contents, your browser will show you Mixed Content Error warning.

2. This happens while browsing that particular web page of your website which contains both secure (HTTPS) and non-secure (HTTP) contents.

3. All the pages using HTTPS address should have only the secured source. Any web page that links to HTTP source will be considered as insecure.

4. You can get rid of the mixed content error by finding and replacing all the HTTP contents of your web page with HTTPS.