I have read a FAQ: If you try to add a folder to BitTorrent Sync and you see this message, it's likely that you've already used the "secret" you're entering for one of the other folders you're currently syncing. It's not possible to sync two separate folders on the same device using the same "secret". But this is not my case... I have directory containing about 60,000 files. Which according to FAQ should not be a problem. It is syncing fine, but GUI shows error BitTorrent Sync cannot identify the destination folder. Nevertheless directory is syncing fine, or at least I haven't found any