Are you using a firewall? Even if you have it configured properly, downloading from other firewalled users will be unsuccessful. If you're not behind a firewall, make sure that you are sharing files with the community. Many users block other people who do not share.

Does nothing here help? Try downloading from a modem user. Does it fail? Most often, they aren't firewalled. A modem user should be able to upload to you just fine.

Please give some more details about the problem if you continue experiencing this. :-)