the Unsecure page error occurs on an https page that is calling content using a full url to an http resource.
some of the resources for the casebook like and share buttons are stored on the facebook server.
for example the following script tag will be added:
<script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script>
since this is calling the script using the http protocol, it causes the error., change that to connect to facebook using the https protocol instead:
<script src="https://connect.facebook.net/en_US/all.js#xfbml=1"></script>
to correct the problem.