We introduced support for IE10 in 2012.2.815 and you are using an older version of RadControls for ASP.NET AJAX, which does not support the IE10.
The recommended approach is to upgrade to the latest version of RadControls for ASP.NET AJAX, but if you are currently unable to, you can render the page in IE9 mode using the meta tag below:
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE9" >
the Telerik team
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