NcFTPd general.cf file configuration
Don't forget to restart NcFTPd after modifying the general.cf file.
Your kernel may not be tuned to handle a large number of active sockets. One symptom of this is if you see error messages saying out of buffer space in the logs (that message comes from the operating system when the server tries to allocate a new socket).
One thing you can try is to have the sockets use smaller buffers. The default socket buffer size is typically 8 kBytes for receive and 8 kBytes for send. Set the reduce-socket-buffer-memory variable to yes if you would like the server to try to reduce memory usage. That is done using the SO_RCVBUF and SO_SNDBUF socket options, which may not be implemented, or worse, not implemented correctly. If you try this, be sure and test that the server still works with it on.
The best way of course, is to properly tune your kernel if you plan to run a high-volume server.