This error has been reported to sometimes occur when trying to activate our latest release, Plex.Earth 3.2:
In order to be able to complete the activation, please do the following:
1) Instead of entering your subscription code, select to start a new trial session
(choose the 24-hour trial to avoid needing to register)
2) Close the pop-up and click on "Service Account", on the Plex.Earth ribbon. Then click on "Activate" and paste your subscription code. You are now ready to use Plex.Earth normally.