When I select the button to open the combo box, there is only a small window/drop down. Two see the 2nd member, I have to scroll down. To get an idea of what I mean, I have attached a screenshot.
Have you set the Height property of RadComboBox? If yes, please remove that and see whether it helps because the dropdown height will adjust according to the number of items (if not set the Height property). Can you paste the aspx that you used if this doesn't helps?