From memory
In the server manager, go to Remote Access
1. Make sure FTP access is set to Allow Public Access, (entire Internet), (I'm assuming you are wanting to access it remotely)
2. Make sure your Secure Shell Access is set to Allow Public Access, (entire Internet),
3 Make sure your SFTP client is trying to connect via the SSH port set unter the Remote Access heading.
If you don't want to do it remotely, but just over your LAN, & you don't want to allow access via the Internet, amend points 1 & 2 accordingly.
HTH
Peter