The system sometimes gets confused. Try explicitly deauthorizing the computer (ctrl-shift-D to ADE) and the device (ctrl-shift-E to ADE when the device is plugged in).
Restart ADE, and see if the authorization can work any better.
You have a maximum of 6 computers/devices for an ID. Maybe with old devices you are trying to get more than 6?
If so, you must contact Adobe service (live chat is easiest http://www.adobe.com/support/chat/ivrchat.html ) and ask them to deauthorise all devices.
You should then be able to reauthorise those computers/devices you still need.
does work. thanks