In ascx(control) dropdownlist selected index event not fired

I am Using control ("ascx") and also i have placed it into aspx page

My Issue is

I have 2 dropdown 1 of them fill at page load event and other or second one fill according to value of first dropdown

When i select 1st Drop down It selectedchange event doesnot fired to fill the other 1 .And also its all item get removed

why its happening???

I have set auto postback property true but nothing its workin for me and when i copy all code on page its working(not to place control ascx)