ANSWER:

inetd is stopping your ftp-service for some reason. This happens a lot when you have too much open connections at any given time. It assumes you are under attach.

Have a look at /etc/inetd.conf. There should be an option called protocol for the ftp-service followed by a number, try setting this higher.

ftp     stream  tcp     nowait/3/10  root    /usr/libexec/ftpd       ftpd -l

The 3 stands for the max number of child processes and 10for the max number of connections. Removing this or changing it to 0 will make this unlimited.

Some FTP clients open a load of separate connections for each transfer, this might cause this behavior.

Don’t forget to restart inetd after making the changes.

by Bart De Vos from http://serverfault.com/questions/389648