When I downloaded the new versions of Revit 2011, MEP would not let me download the content, at least not all 16 bundles. I thought maybe it was my ISP cutting me off with a large bandwidth download. I thought all sorts of things. I ended up getting my content from the media when it arrived, yes I asked for the DVD, how can you collect them if you don't get them?
Long story short - I thought I disabled my anti-virus software adequately. Turns out that I did not. When I carefully shut down each of the services that were running (leaving me temporarily vulnerable to internet evil) the content downloaded successfully!
Next time you are having issues, remember the often stated and repeated mantra of disabling the software you use to protect you from internet evil. I happen to be using AVG's products so your mileage may vary.