I tried using the Expander pretty much as is (as a test to understand control) and got and error saying SL plugin must be set to windowless? Also said, to put RadEditorHelper.xap in the client bin directory which I did. My WCF app is the host (not ASP.NET) but i specified attribute [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]. Not sure this attribute is needed or not for Telerik expander?
What I really want to do is have an expander followed by a datagrid. I want the datagrid when the expander is collapsed to use all the screenspace under the expander header. When the expander is expanded I want the datagrid to move down leaving space for the expander content.
Hope this is something that can be done, If not is there an alternate technique.