It happens to me that ftp on my server, that has always worked fine in remote in passive mode (having on the router the port 21 open) suddenly it has stopped working.
It now works only in active mode, also opening the port 20.
I have tried from the same computer to access the service ftp of the server of one colleague of mine and his continuous to work in passive mode, therefore I exclude a problem of my workstation.
OSX server 10.4.4