Thank for the additional info.
I have a general question regarding loading the user control. I am following your example in http://demos.telerik.com/aspnet-ajax/tooltip/examples/tooltiptreeview/defaultcs.aspx
Everything works fine when the tooltip needs to be loaded. The OnAjaxUpdate event fires correctly and I load the usercontrol. In the Page_Load of the usercontrol I set the Text of the TextBox with the current time. I then Cancel the tooltip and open a second one. The time is the same in the textbox and is not updated with the new time. Even-though in the debugger the value has changed the textbox does not get updated.
If I move the code of updating the textbox from Page_Load to Pre_Render the time gets updated correctly. I am wonderying why the textbox does not get updated on PageLoad.
This may have to do with the Update Panel have UpdateMode="Conditional".