I have already had to update my UsersOnline module to cope with a similar problem, the HostSetting 'DisableUsersOnline' in DNN4/5 changed to 'EnableUsersOnline' in DNN6!
I saw your forum post on the DNN forums. I'll bring that issue up today as well. They shouldn't be changing key names. That makes it much more difficult for module developers to support multiple versions with the same code base.