When using the Flash Manager to add a flash object into the content, causes the HTML mode to be non editable. The following example code is a possible workaround for this behavior: <telerik:RadEditor ID="RadEditor1" runat="server" OnClientModeChange="OnClientModeChange"> </telerik:RadEditor> <script type="text/javascript"> function OnClientModeChange(editor, args) { var $ = $telerik.$, mode = editor.get_mode(), contentAreaElement = editor.get_contentArea(), editorModes = Telerik.Web.UI.EditModes; if (mode === editorModes.Html) { $(contentAreaElement).hide(); } else { $(contentAreaElement).show(); } } </script>