How to register a postback in a RadscriptManager, to preserve the value of a FileUpload that is contained in a RadAjaxLoadingPanel.
This in an example using ScripManager and UpdatePanel:
Protected Sub BtnSubirFoto_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles BtnSubirFoto.PreRender
Dim btn1 As Button = DirectCast(sender, Button)
Dim rsm As RadScriptManager = DirectCast(MyMaster.FindControl("RadScriptManager1"), RadScriptManager)
rsm.RegisterPostBackControl(btn1)
End Sub