Nothing worse than trying to debug FTP (File Transport Protocol) issues in the presense of firewalls.
FTP is a really old protocol that due to the way it works, makes it difficult to support properly when there are firewalls at both the client side and the server side, primarily because by default, whenever the server wants to send data to the client, the server initiates a connection back to the client. Sure, there's passive mode, but that just means that the server tells the client to connect on a different (and usually blocked) port on the server for the data.
It's especially frustrating when these things suddenly stop working.
Grrrrr.