I am using the trail version of the controls. Loading a Tree on Demand using Server Call pack method. Doing so I get this ugly error:

sys.webforms.pagerequestmanagerparsererrorexception: The message received from the server could not be parsed. Common causes for this error are when the resonse is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled. Details: Error parsing near 'Telerik.Web.UI2009.'