Problem downloading zip files - php

There is a problem downloading .zip files from my site. Site is here: hiokiusa dot com at the bottom right there is a section called Software Downloads (view full list). The file will download in the browser, but when you try to open it, it is corrupted. I believe this is a problem with the headers. This needs to be fixed so that files are downloadable without corruption. Currently the 'resources' download section works, fixing the software section should not effect the resources section. Both should be able to download uncorrupted files. Let me know if there are any questions about the project.