When a RadButton with a PostBackUrl property set is located inside an UpdatePanel,  it does not redirect to the PostBackUrl on click and a JavaScript error message is thrown.

The workaround is to use:

- Either a RadButton (ButtonType="LinkButton") and set its NavigateUrl to the desired page that is to be redirected
   
-OR a RadButton (ButtonType="StandardButton") and use its OnClientClicking event handler to cancel the postback and redirect to the desired page through window.location.href. For example:

    <script type="text/javascript">
        function OnClientClicking(sender, args) {

            window.location.href = "http://www.bing.com";
            args.set_cancel(true);

        }
    </script>