DropDownlist autopostback

i have four ddl's .
all of them autopost = true
when first ddl changes , the other three also need to be chaged... data comes from database.
this works fine when i manually change the first ddl.
 
while at runtime when i pass the value to first ddl the othere four don't changed... i even don't get into the SelectionEventChanged of the first ddl.
 
i am really stuck here.
 
any clues?
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