I know that such question was has been many times already but I couldn't find any right solution for my problem.
I have MasterPage1 with ScriptManager. There is MasterPage2 in it. In 2-nd MasterPage I placed Control with UpdatePanel. In this UP I placed FileUpload and SubmitButton:
Master1(with SM) <= Master2 <= Control(with FU and But)
I tried to debug method But_OnClick and saw that FU.PostedFile == null.
I tried to place PostBackTrigger to But in UP, I tried to do it from Control's code behind using something like Page.Master.Master.FindControl("ScriptManager") and it doesn't work.
And I even tried to use AjaxControlToolkit...