Check with them and see how they are trying to download the files and whether they are using a download manager of some type.
Most of you know my site http://www.wayne.hardy.com I have a Download page that contains free software. I'm getting reports that when someone tries to download they get a zero byte file. An example is this one for PrintNow http://22.214.171.124/software/PCMPRNTN.ZIP
I can download it from three PCs running XP and W98SE but a visitor said they couldn't download it.