Uploading is fine, downloading is not.

Hey there everyone. I have a custom program that is basically just an FTP server which is giving me problems. I have narrowed it down to some kind of a network/router problem, as the software works fine from multiple other locations. The only problem is with downloading files. Anyone can upload files to the server just fine, but any attempt at downloading a file over a few hundred kb and it just hangs there indefinitely. I have scoured every router setting, made sure there is no conflicting software on the machine(Its a completely clean XP Pro install with nothing more than drivers and this program installed.), configured(and even turned off entirely) the windows firewall and all that noise. I just cant figure it out for the life of me, and I am basically just looking for anyone that has had a similar problem and what was giving them trouble. Thanks in advance for any, and all, help.