We had a problem with Virtual Machine which Cisco Virtual WLC installed. Virtual Machine files were damaged and the system was not start normally. We have had to reinstall the WLC, but after installation impossible to import current license to new one.
Licenses are tied to the device they're being used on. With a virtual WLC, the license is tied to the unique identifier of the vWLC and when you recreated the vWLC after your VMware problems the new vWLC has a different unique identifier.
It's a similar situation to what happens when a physical controller is faulty and is swapped out by cisco, the replacement will have a different serial number and you'd have to re-host the license to the new serial number.