I rather rashly upgraded my second machine to Sierra. LR was version 6.6 and as soon as I opened it it said that I had used up my licences and had to deactivate another machine. I then updated to 6.7 and still have the same message. I've reinstalled several times but still get the same message.
I only have it installed on 2 machines and this was the second one and it worked perfectly before the OS upgrade.
I can see no way to 'deactivate' the copy on the laptop in the hope that it might reset my licences numbers. This is a standalone version.