I realized that the cause is a change in the server. We use a VPS, we changed it from OpenVZ to Linux Containers and the MAC address changed.
With OpenVZ the host share la MAC with containers, with Linux Containers each interfaces inside cotainers has a own MAC address. And centova associate the license with domain and IP+MAC.
The hostname and IP didn't change.
I tried with button "re-issue" in my client area but the license remains invalid.