Basically, when you buy a Cobb AccessPORT unit and install one of the maps onto your car, the unit becomes "married" to your particular car. This means that the AccessPORT unit can not be used to load a map, check engine codes, monitor data, etc. from any other car while it is still "married" to the first car it was used on. In order for it to be used on another car, it must first be "unmarried" from the first car, meaning whatever map was loaded on to the first car must be uninstalled, or "unmarried." So basically, the first car will be reverted back to stock and at that point, the AccessPORT unit will be able to be installed/used on another car - or "married" to that car. Make sense?
If you buy a used AccessPORT, it is very important that it is unmarried from whatever car it was previously used on. Otherwise, it will be useless to you and you'll have to send the unit to Cobb and pay an expensive fee to have the unit refreshed - for lack of a better word.