All packages are up-to-date, I am using VirtualBox 5.1.10
Uname: Linux laptop 4.8.8-300.fc25.x86_64 #1 SMP Tue Nov 15 18:10:06 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
When I click on:
- Menu: Preferences
- Tab: Extensions
- Button: Adds new package.
It works if I choose "Gnome Xorg" when opening the Linux session.