I am using the latest version of telerik controls (2010, 1, 519, 35). The page I am having a problem with works fine when I run on my local IIS (v5.1) and fine when I run from inside VS2005/2008. The problem is that when I promote the code to Winhost this page is failing, in the following manner: Treeview displays on left, when an item is selected in the treeview there are 3 radpanes on the right that need to be refreshed. The first time I click on an item in the treeview it works fine, when I select a second item nothing is refreshed and the following error is reported on the page: Object doesn't support this property or method. Normally, this means I typed a client side method incorrectly. But I didn't. And the first item I selected worked fine. When I comment out the AjaxManager, it works all the time. Did I forget something in my depoloyment ? Any help would be greatly appreciated.