Strange FTP Error Only On One PC [Help]!

I've used FTP programs for some time to upload files to my web pages. Recently, I added another PC to my LAN to host online games for a small group of friends. I decided to log game stats and I wanted to upload them to a web server via an FTP program with a scheduler function.

I can connect and access all web server files (and can delete/move, etc.), with no problem, however, my FTP uploads fail every time. I tried this on this same computer with several FTP apps, and with all of them I could connect and manipulate server files, but could not upload. In contrast, I can upload with no problem from other PCs on my LAN using WS-FTP (and any other FTP program), and I can upload files from other PCs not on my LAN to that same web server--just not from that server PC where the logs reside. Anyone have any ideas--I imagine it's some stupid Windows setting, but which one?