Have a look at these links, Paz:
https://helpx.adobe.com/x-productkb/glo ... mbers.html
https://www.adobe.com/genuine/landing-d ... d=791Y6S4Z
https://forums.adobe.com/thread/2352426
It has been found that some less than honest owners of volume licenses have been selling them (not legal to sell a volume license) and as Adobe finds these they are flagging the serial numbers.