The software needs to verify the subscription is still active approximately once every 30 days. It needs to be able to contact our servers in order to do this. That error message indicates that some part of the process was unable to be completed. If they were able to successfully activate the software at the time they first installed it, then perhaps some setting in the network has changed.
I would advise the user to review the Firewall settings documentation: Firewall settings required to unblock ANSYS Discovery Products