Have you recently restored files onto a Mac using Time Machine? If so, that may be the cause of this cryptic activation error.
You MUST first be logged in as user that has administrator access. (if you only have one user / login on your Mac, then that account will be your administrator).
Download the attached file and unzip the file to the desktop. It will be called cleanup.command. Double-click the cleanup.command file to run, then follow the instructions that will be displayed.
Now try activation. If it works, please DELETE the cleanup.command script and the cleanup.command.zip archive. They should never be run EXCEPT by direction from us.
If this does not work, please create a support ticket and we will investigate your particular issue.