AMS server is asking for a new activation key, can you explain why?

For your information,the AMS's Product Key was generated from PC's Mac Address.

So if the client had migrated the AMS installation to the  new PC,the AMS Product Key will be changed again due to different Mac Address. 

Or the client had two LAN cards at the same AMS installation PC.So when the client disable one LAN card and enable the other one,the AMS Product Key will be changed in this case.

Or if the client is running AMS at Virtual Machine,please make sure that the VM's network card (MAC address ) settings should be 'set to 'static'' not dynamic.