I installed it once, but the thumb drive it was installed to was filling up from indexing my NAS. So, I deleted the directory (/mnt/DATA) it was installed to and everything seemed to be fine. Even the "Extensions" menu in my NAS4FREE web GUI disappeared.
However, any subsequent attempt to install it again somewhere else just hangs (no CPU usage).
Running /mnt/DATA/extensions/bts_install.php gives this error (i replaced DATA with the correct file path, but for writing my fix here, i'll use "DATA"
Fixed by cp /mnt/DATA/extensions/btsync/version.txt /mnt/DATA/extensions
Restart
re run the two install commands