The latest build of RadEditor for MCMS (Premium) is 7.3.4. It is built on 8/14/2008, which means that it does not support IE8.
Is it possible to add a meta tag in your MCMS pages so that the page is rendered in IE7 mode, this would be much easier than fixing the problem in the source code:
<meta http-equiv="X-UA-Compatible" content="IE=7" />?
Your company has bought a license for RadControls, so if you would like to obtain the source code of RadEditor for MCMS (RadEditor_PremiumPlaceholder_7_3_4_Source.zip), please, open a support ticket and request it. Note that we do not provide support for MCMS as well as source code modifications.
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