The error is Sys.InvalidOperationException: Sys.InvalidOperationException: Component 'RadEditor1_dialogOpener' was not found.

When not enabled RadEditor should merely show its content, when Enabled is toggled to true it should render toolbars and add its functionality.

A possible workaround is using the Visible property instead and a div with runat=server as a placeholder for the editor while it is not rendered (its Content property will still return the HTML in it). Thus, the innerHTML server property of the div can be used to set the HTML from RadEditor in it.