I received the error message "Invalid activation file"

First thing to check, do you have the latest version of Circle installed? It's always available here: https://futureaudioworkshop.com/downloads/

If that doesn't work...

1. Copy your custom presets on to the desktop. The presets can be found in (Mac) "Macintosh HD/Library/Application Support/FAW/Circle-2/Presets" or (Windows) "C:\Program Files\FAW\Circle2\Presets".
   
   
2. Delete the Circle program folder: (Mac) "Macintosh HD/Library/Application Support/FAW" (Windows) "C:\Program Files\FAW\Circle2".
   
   
3. Reinstall the latest version of Circle, it's always available at https://futureaudioworkshop.com/downloads/ 
   
   
4. Reload Circle and you should be able to activate successfully!
   
   
5. Copy the custom presets that you place on the desktop back into the Circle program folder.