When using Windows Explorer on both Windows 7 Enterprise and Windows XP professional, the download stops at 48 MB. The full download is supposed to be 4.04 GB.
I tried using a recommended Download Manager (Free Download Manager) but that doesn't work at all. Oracle's website requires authentication, but it does not accept my credentials when submitted through the download manager. Even if I login before downloading, the download manager cannot receive any part of the file.
This is not just a problem with my site, as others on the OTN forums have the same problem. See message: Re: Can not download Oracle_Developer_Day.ova
When you try to import the partially downloaded .ova file into VirtualBox, it says the file is corrupted.
Windows Explorer or Microsoft Explorer are known to doesn't download correctly large file and this is not only the case with Oracle files. Try to download it with Firefox (tested now with the above URL and it works).