I get the error message 'Invalid Product Key - Couldn't write to PREF-file' when Activating NTFS for Mac

Trying to activate NTFS for Mac results in an error message

Typically this error results from incorrect file permissions or an existing settings file that has become corrupt. A new settings file will be automatically generated if one doesn't exist, so it can be safely removed.

How to remove the existing settings file

• Open Terminal (Applications -> Utilities -> Terminal)
• Issue the command:
  

  sudo rm -f "/Library/Preferences/com.tuxera.NTFS.plist"

If the problem persists, you can contact our support team at macsupport@tuxera.com