I upgrade to IE 10 today and was debugging my website that uses Telerik AJAX Controls (Version 2011.2.915.40) and am getting a
JavaScript runtime error: Unable to get property 'documentElement' of undefined or null reference
this happens when I click the arrow on the RadComboBox (also happens when I hover over a RadGrid).
I noticed that it happens only when I am debugging the site on IE10 (Even happens if I choose 'Start without debugging' option in VS 2010). I found that the java script error is occurred inside dynamically loaded java script file “Telerik.Web.UI.Common.Core.js” at statement (var C=a.document.documentElement
If I host the site on IIS 7.5 and open it in IE 10, then I don't get the JavaScript error, however the RadComboBox does not drop down.