RS300 connects by LAN but not by internet FTP

I have set up my RS300 (Firmware Version V1.0.1.60), from my Mac, as shown in screenshot attached.

The Mac reads the local share "readyshare" no problem, but I cannot get any kind of ftp connection to the readyshare volume.

I'm using dynamic dns to point to my router, and I know that works because fileZilla reports resolving my dynamic url to exactly my routers ip address.

Using fileZilla I get the following errors:

Status:      Connection attempt failed with "ECONNREFUSED - Connection refused by server".

Error:         Could not connect to server

Status:      Waiting to retry...

Status:      Connecting to 192.168.1.1:21...

Status:      Connection attempt failed with "ECONNREFUSED - Connection refused by server".

Error:         Could not connect to server

Status:      Disconnected from server

Status:      Connecting to 192.168.1.1:21...

Status:      Connection attempt failed with "ECONNREFUSED - Connection refused by server".

Error:         Could not connect to server

Status:      Waiting to retry...

Status:      Connecting to 192.168.1.1:21...

Status:      Connection attempt failed with "ECONNREFUSED - Connection refused by server".

Error:         Could not connect to server

Any clues what I'm doing wrong?

 - Thom Walker