I found a solution! Well at least it works for me. I have a shared Videos folder on my Synology NAS which I wanted to sync between my Mac. I also had the problem with permissions. So I went to the Control Panel – Group – Users – Permissions – and ticked the Read/Write option for the Videos folder which I wanted to sync. And now the Bittorrent Sync client on my NAS indeed syncs the folder. The permission problem is gone. Really happy about it! . I hope it works for you. : ]