If you're having trouble downloading you need to:
1. Clear your browser cache.
2. Restart your computer.
In some cases you might be able grab everything at once with no problem. In other cases you might have to wait a day and then retry certain files, clearing your cache every time. I would avoid trying to download during peak business hours in the US - 8am EST - 5pm PST.
I know it's not the most graceful system, but it allows me to track the number of downloads per file, plus it's free. If I was hosting the files on my own server I'd soon be overloaded with requests and have to start paying my host for going over my monthly limit of downloads.