I have a RadToolbarDrorDown that allows users to select a different theme. This works fine in Firefox and Chrome, but the dropdown fails to show in IE (v10). It does appear to work with IE 9.0.8 however. In IE 10 I see this script error in the console: SCRIPT5007: Unable to get property 'documentElement' of undefined or null reference ScriptResource.axd, line 147 character 2 Also, the html generated is quite different : see attached Telerik version 2012.1.215.40