NcFTPd general.cf file configuration
Don't forget to restart NcFTPd after modifying the general.cf file.
This controls whether remote users are allowed to append to local files when uploading using the APPE command. If you disable this, users may have trouble resuming uploads if their FTP client program uses APPE rather than REST with STOR.
Unless you're sure what you're doing, leave allow-append set to yes.