If an error code is generated / returned by the server, it will be included in the log output. It won't be shown to the user (since a FileTypePlugin isn't allowed / able to show a popup message), but it can be seen in the log.
In this case, the plugin can't even send anything to the server as it fails to decrypt some of the activation information, so there's no error message for it to generate. In the next version it'll print a more useful error message (like "Authorization corrupt, try to re-authorize) into the log.
As for the adobe error codes, I've started a list of all of them I could find during development of this plugin:
https://github.com/Leseratte10/acsm-...be-error-codes
Though, most of these are errors a normal end user will never encounter.