Dropdown list is not firing

In Page i have 3 dropdown, first am initializing on page load which is working fine,am getting required value on pageload.

2nd dropdown is value is dependent on first dropdown. am setting Autopostback = "true" and OnSelectedIndexChanged for first dropdown, and on change of first dropdown am displaying required value in second dropdown, it is working  fine and also OnSelectedIndexChanged,Autopostback working perfectly fine.
 3rd dropdown value is dependent on second dropdown, am setting autopostback,onSelectIndexChanged for second dropdown, but third dropdown value is not displaying. Autopostback,onSelectIndexChanged is working fine for first dropdown but not for second(but it is same as first,but not working..!), onSelectedIndexChanged  is not working for second dropdown(if in put breakpoint for code, it is not going inside the function.)
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