The RadXmlHttpPanel uses either ASP.NET client callbacks
or Web Services to update its content. This means that the lifecycle of the page is wholly dependent on this technologies.
The Web Service is a lighter than the ASP.NET client callback, because only the object passed to the set_value method is sent to the server. In the case with the callback, the values of all FORM fields, such as hidden fields (including the view state field) are sent to the server.
This being said I believe the Web Service approach will be the one to take. Here is a tutorial from our online documentation, that shows how to configure the XmlHttpPanel to work with web service: http://www.telerik.com/help/aspnet-ajax/radxmlhttppanel-webservice-configuration.html
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