Hi
Did you verify with following commands to see if there are any wireless users still using?
display wlan client
display portal user all
Did you use the "portal delete user-all" command under the "enable" mode to try deleting the user?
Alternatively you can look at adding "idle cut" command under the portal domain, to delete/remove the user from the data base if there is no activity after certain period.
http://h20564.www2.hpe.com/hpsc/doc/public/display?docId=mmr_kc-0126307