Robyn,
sync2nas uses the rsync protocol on port 873, which will work fine over a local network. However, sync2nas does not support SSH, so when you try to connect from a remote location your SME server blocks the sync2nas connection attempt at the firewall level. This will show up in your server logs like this:
May 24 09:48:23 kernel: denylog: SRC=64.25.xxx.xxx DST=216.75.xxx.xxx PROTO=TCP SPT=1092 DPT=873 WINDOW=16384
Of course, that's been abbreviated, but you get the idea.