ecDownloads 4.1 has two known security leaks. Because of this the mod is taken down from vB.org
There is a forked version:
DownloadsII. It fixes the security issues, a lot of bugs and adds some new features. You can upgrade without any problems from ecDownloads 4.1 to DownloadsII 5.0.2.
For your problem: upload a blank index.html to your downloads folder. Normally it's
www.yoursite.com/forums/downloads/, but I see that you have changed it on your site.