If you want to load an initial user control, I would suggest that you do it in the Page_Load server event. If you use the selection changed mechanism for loading the initial user control, you make an unnecessary postback. Try the following:
1. Extract all the code from the RadListBox1_SelectedIndexChanged event handler in a function, and in the handler just call the function. You can pass the index or value to the function, to determine which listbox item was selected
2. In the Page_Load event handler, if the page isn't a postback, call the same method (with argument 0, if you are using index to determine the listbox item)
Hope this is helpful.
the Telerik team
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