Thank you for contacting the Telerik Support.
Judging from the screenshots which you have attached it seems that you are pasting some images in the RadEditor. Could you try pasting them one by one and execute the filtering each time in order to see if a specific image triggers the error? In addition, could you try this scenario in other browsers except from Google Chrome and inform me if you are able to reproduce the same issue?
Furthermore, could you please provide me the exact HTML content which you paste in the RadEditor? This will help me to investigate the matter and give you further details about it.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed