Kolloquia

… and then the download fails.

You’ve experienced this problem with VirtualBox or are stuck just at the very moment you’re reading this post here? Here’s the solution:

https://www.virtualbox.org/wiki/Testbuilds

Click on the link above! At the bottom of the page you’ll find this:

Both tables offer a download link for the image file of the Additions CD/DVD. Download it and load it, that’s all!

I strongly recommend using the Development snapshot!