Telerik RadAjax controls won't work in browsers that do not support XmlHttpRequests. You may want to disable AJAX when such a browser opens your site. To disable AJAX, you can set the EnableAJAX property of Telerik RadAjaxManager or RadAjaxPanel control to false both on client- and server-side.
The .NET 2.0 framework provides the SupportsXmlHttp property and it should be used to check if the browser supports XmlHttpRequest :
RadAjaxPanel1.EnableAJAX = Page.Request.Browser.SupportsXmlHttp;
RadAjaxPanel1.EnableAJAX = Page.Request.Browser.SupportsXmlHttp
When this check is made in the Page_Load event handler, it will make your page work as if it was in a standard postback scenario for those browsers.
Some browsers do support XmlHttpRequests and still return false for the SupportsXmlHttp property.In such cases, you should define Browser definition files. You can find more info in the links below.