When using Active Directory with NS4300N/NS2300N (this means NAS Device is part of Active Directory Domain), FTP File Sharing is disabled if the service was already enabled. Any attempt to enable FTP File Sharing will result in the service being disabled. This behavior is "by-design" as the Active Directory Domain Controller is in complete control of User and File System Access to the NS4300/NS2300N. Active Directory and Windows feature a very complex file security protocol and attributes, enabling FTP with Active Directory will result in conflicts and also compromise overall security.
If you want to use the NS4300N/NS2300N as an FTP with Active Directory enabled we recommend using Windows FTP Server (allowing Windows Server to Control FTP Access) with the NS4300N/NS2300N as the Storage for the FTP.