I have just installed my livebox and mates come round and can't log into the wireless system - a message pops up which says they are not on the access list that the administrator has set up - what is this list and how do I sort this out please?

I have just installed my livebox and mates come round and can't log into the wireless system - a message pops up which says they are not on the access list that the administrator has set up - what is this list and how do I sort this out please?
Edit/Delete Message