Please log into ADM Administrator and confirm if your licence is still valid. If it has expired, then it will give you a prompt on login to request a new licence, which can be done so by emailing [email protected]
If your licence is valid, then this is likely caused by a Windows update on your IIS server where the ADM Web service is running, we have identified that it is caused by
Windows Server 2012
Update for Microsoft Windows (KB4565635)
Update for Microsoft Windows (KB4565613)
There is a configuration to the ADM web service that can resolve this issue please raise a new case online and one of our Technical Support Engineers will apply the fix for you.