Windows needs to connect to the license server on campus every 180 days in order to stay activated. After that time, users will start to see this message if the computer hasn't been connected to the on-campus network or VPN.
This issue is usually resolved by connecting to the on-campus network or connecting the the VPN if the machine is off campus. Leave the computer connected for at least 3 hours to insure that it has had a chance to check in with the license server.
More information and troubleshooting steps are available at https://it.purdue.edu/shopping/software/instructions/windowskms/index.html