Symptom:

You have HTTPS/SSL enabled on your site but when you access a page via https://yoursite.com/somepage your browser prompts you with "This page contains both secure and nonsecure items".

Resolution:

This is not a server side issue - it's due to how you have content referenced within your webpages themselves. I.e., it means that you have embedded content in the page (like an image or a javascript, that's referenced as http://somewhere/someimage.jpg).  The inclusion of this embedded element with http (instead of https) causes that item to be sent to the browser via http, not https... hence, some of your page is sent to the browser via https, and this element sent by http... and results in this "some secure some not secure".

To address this issue, you need to modify those pages which have elements referenced via HTTP by either:

1. changing the link to include https instead of http.  For example: change img src=http://somedomain.com/image.gif to img src=https://somedomain.com/image.gif
2. if the linked content is on your site, use relative paths instead of absolute.  For example: change img src=http://yourdomain.com/image.gif to img src="image.gif"

One of the quickest ways to find these elements is for your website developer/admin to open their local copy of your website files, and search them for any instances of "http".