Alright, here's the thing. I recently got into "PSX" emulating, and wanted to download Chrono Cross. But when I tried downloading, It gave me a "Some files don't allow you to download twice" error on my download manager (Internet Download Manager) and after that, I tried refreshing, and RomUlation gave me that message where I can't download two files at once when I was not even downloading anything. Edit: I was using the US Server, I am downloading it now from the European server. I still would like to know what causes this problem though.
It could be that the server opened a connection to you and it took a while to reset it to allow you to download another.
Are you using Chrome? Internet Download Manager (IDM) works fine for me in IE and Firefox but not in Chrome. I have to right click the link, copy it and paste it into IDM for Chrome. =/