Your going to need to give a little more info as to whats going on. Nothing showing? Or just username not showing? Give as much detail as possible, will help us in helping you track down the problem.
Also check the fields you have in your list to make sure you have them set as searchable.
Following fields are in list but not visible in here for following reason(s):
Field "Username (username)" is not displayed on profile !
If you save list now, they will be removed from the list. If you want to keep them, cancel now and go to Components / CB / Field Manager.