Error in Internet Explorer "Only secure content is displayed"

Environment

Product	Progress® Telerik® Reporting
Report Viewer	HTML5-based Report Viewers
Browser	Internet Explorer

Description

The HTML5 Viewer is a client-side widget consisting of Kendo UI widgets and functionality for communicating with a Telerik Reporting RESt service instance. The Ui and the functionality are added via JavaScript and CSS files loaded on the same page. The error is thrown when you try to load a page with the HTML5 Viewer.

Error Message

 "Only secure content is displayed"  

Cause

 
If you use an IFRAME element to load the page with the HTML5 Viewer, and all requests are issued over HTTPS, the error can occur due to a left link that uses HTTP.

Solution

The issue can be detected by running the page in Internet Explorer with opened Console (F12 Developer Tools). In the error logs you will see a message like the following:

HTTPS security is compromised by http://kendo.cdn.telerik.com/2015.3.930/styles/kendo.common.min.css

This will hint you which CSS/JS files are requested over HTTP.