The Bitlog WMS license is only possible to have activated on one server at a time. 

This is done through a validation against the Server where Bitlog WMS is installed. And if the server is changed in anyway, Bitlog will class the server as invalid and therefore the license needs to be activated through a migration in Bitlog WMS Manager client.

In details WMS is performing a control of current hardware (CPU, BIOS etc) as a combination to find a hardware fingerprint.

Examples for when hardware fingerprint can change:
If Wms App server is running as a virtual machine, and then machine CPU, RAM or something similar are changed then fingerprint is changed, and then the Wms License needs to be migrated to the server again.

If Wms App server is moved to a new hardware the license needs to be migrated.