It looks like the DocumentManager and ImageManager (part of the RadEditor) are not working at all when using Internet Explorer.
The page says "This content cannot be displayed in a frame" and in the IE Developer Console I see the error "SCRIPT5: Access is denied. Telerik.Web.UI.WebResource.axd (16532,28)"
I have attached an image showing what I see.
I have done some looking around and it seems like this issue was supposed to have been fixed since ASP.NET 3.5 was released. We are targeting .NET 4.6.1
Our Telerik DLL version are a bit out of date but we are no longer paying for the product so cannot get the latest versions. We are currently on version 2014.2.618.45.
Below is the the simple code I have on a ASP.Net WebForm that we have the editor on. When I view this editor in IE I get the error described above and shown in the attached screenshot.
Thanks in advance.