richfed,
Please try this, go to this folder: C:\ProgramData\Stardock (note: ProgramData is a hidden directory, you need to set File Explorer option to unhide hidden directory.
Once you get to that directory. Delete off all Fences directory. For example, from screenshot below, all folder with red need to be deleted.
Once that is done, try to activate again.

Note: Moving forward please report back here for these specific issue: https://forums.stardock.com/535207/fences-6-212-activation-issues
Thank you,
Basj,
Stardock Community Assistant