I removed the old version of btsync on the RPi and installed the latest version (from the repositories) and it seems to be working now.
Question: I am sharing my Win10 folder as read only with the RPi. If I delete a file on the RPi, I understand it won't delete it on the Win10 machine. But will it ever "reappear" on the RPi? I'm using btsync as a remote backup solution for all my family photos. If something on the Rpi gets corrupt or deleted, I don't want it to corrupt the version on my Win10 machine, which is why I use ReadOnly. But at the same time, if I accidentally delete something on the Rpi, I would like it to automatically get replaced by the "good" file on my Win10 machine. Is that possible??