Can't upload file to from a corporate environment

I am using this loader successully in a non-corporate, non proxy environment and it works great. However, my client, who has a firewall, proxy server, pretty much, a good security network can't even upload the file from their pc to my web server. What setitngs do they need in order to upload a txt file to my webserver. I am using port 80 and they have rights to write a file to my webserver.

Please help is greatly appreciated.