Most common reason this issue will occur after a return merchandise authorization (RMA) has been performed. When the new device is received, new licenses must be generated to match the new hardware id. For RMA license generation instructions, refer to KB40023 - [Customer Support Tools] How to generate an RMA license using the Licensing & Download Center at my.pulsesecure.net
If the administrator is attempting to migrate licenses to another device, this is not supported. Once the licenses are generated for a specific hardware id, the licenses cannot be migrated to another device unless an RMA is performed.