No I've never seen that particular issue. It doesn't sound too obvious. Is there remote logging enabled? SNMP? Something other than, "one day it stopped working.." ??? There has to be a delta somewhere, maybe something you aren't aware of yet?

As for a proxy that does ftp... Squid could probably do it. http://www.squid-cache.org/ but it's been a while since I used it, so I'm unsure about the command line deal.

Or if you just want to proxy the ftp stuff seperate from the web stuff ftp.proxy can handle, you do need a *nix box though. And as far as I know it's client independent and does command line.

http://www.ftpproxy.org/