See the demo at
http://www.9rays.net/asp.net/treeview/Demos.aspx?demo=program_server_events
Select any node. Click postback page. And see the value at SelectedNodeChanged section. It seems to work.
Also, I noticed that after the init, load and prerender treeview event run, the unload event also launch ?!?
May does it have something to do with my problem ?
No, unload event is ASP.NET infrastructure event and does not deal with treeview events.