virtualbox.org

I downloaded the extension pack but something is wrong. Cannot open file to extract files. Fileroller comes back with unknown file. Please help.

I have found the problem!
On my main computer the extension pack is downloaded as a .tar.gz file.
On my wifes computer it is downloaded as a .vbox-extpack file and asks me if I want to open it with Virtualbox.
I simply saved the file and copied it over to my computer and opened it.

See Ch. 1.5 Installing VirtualBox and extension packs.

I have found the problem!
On my main computer the extension pack is downloaded as a .tar.gz file.
On my wifes computer it is downloaded as a .vbox-extpack file and asks me if I want to open it with Virtualbox.
I simply saved the file and copied it over to my computer and opened it.

Thanks for the reply. But I found the problem on my own. I don't know why it downloads differently on the two computers. Thanks again.

Well, the only ExtPack files available for download from the official site (http://download.virtualbox.org/virtualbox/5.0.12) end in .vbox-extpack. Maybe you downloaded yours from somewhere else? Or your browser/FTP client is playing games on you?

It also happened to me, for some reason while downloading the file on windows the extension is replaced with tar gz (I guess because that's the compression used by the file). Anyway it's enough to rename the extension with .vbox-extpack and it works