DropDownList does not dispay the correct Items

 Hi,
I have a DropDownList  (in an UpdatePanel markup ). I am updating the DropDownList on the server side (when performing OnClick event of a button) I am erasing few items and then add few others.
The problem is that DropDownList doesn?t refresh itself correctly ? the content of the DropDownList  is not accurate. If I am reloading the page (with redirect to the same page) the content is valid. There must be though a cleaner and more professional way to do it, Isn?t it?
 
Thanks
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