http://msmvps.com/blogs/shareblog/archive/2009/03/11/cannot-unregister-updatepanel-with-id-since-it-was-not-registered-with-the-scriptmanager-and-moss.aspxI have run into this while trying to get the AjaxControlToolkit working with MOSS. Turns out there are a couple of things that can cause this. The first is using CreateChildControls to create your controls. While this is typically a best practice in thisenCommunityServer 2008.5 SP2 (Build: 40407.4157)