How can I help my server mate?

I get the software caused the connection to abort on your host machine error. Skimming through a few related posts, I find this is the server's issue and nothing I can do about it. However, I'm in contact with the guy running the server and he can't figure out what's wrong. Does anybody have any idea what kind of typical errors cause this kind of problem on the other end? He's checked his router and and he doesn't have a firewall running. He's using the xlightftp server program. Thanks for any help you can give.