There's quite a discussion on Microsoft forum about firewall:
Can't turn off Win 7 domain firewall
I'm not an expert on Windows and I recommended you switch off the firewall for good measure. It's just a logical step. However, messing with domain controllers in a production environment is not recommended.
It might be easier to take that client off the domain, test ftp, and then put it back on the domain rather than mess with domain settings.
Need a Windows expert.
---------- Post updated at 10:36 AM ---------- Previous update was at 10:31 AM ----------
Another thing I would do is ping the client from the unix box then shutdown the client to check the ping fails just in case duplicate ip address exists. Perhaps when the unix box "calls back" during the ftp it's routing elsewhere and not getting to that client. Just a thought.