3 of 4 computers show in Norton Management under devices

In Norton Management under account it show all 4 of my computers.  Yet under devices it only will only show 3.  Worked with online support for a few days and they could not figure it out.  When I put antitheft on the 4 th computer then the one of the devices will switch under devices.  Then the next time I logon to the computer that disapeared from devices says I need to install antitheft again.  If I do they will switch back.  I can go back and forth all day.  Does anybody have any ideas?