Problem with dropdownlist control

Hi,
   
     I have a problem with the dropdownlist control in my asp.net project.If i select any item in the dropdownlist it is not displaying that selected item,it displays the first index,but when i select any item for the second time it displays the selected item correctly.And I have set autopostback property true and page.ispostback property false also, how to solve this problem.please help me

Thanks in advance