Make sure that you paste the license certificate into the same computer that you did the activation request for.
In other words, the activation request and the license certificate MUST be performed on the offline machine (not a different PC) via License Manager.
Once you generate the activation request from the offline machine via the license manager, you cannot close that window until you paste the license certificate.
If you happen to close the license manager window prior to pasting the license certificate, the process will fail and a new activation request must be generated.
Ensure to copy the license certificate string from our webpage.