VirtualBox package in Ubuntu 16.04 LTS does not successfully install Windows 10 Insider Preview. To install, you need to install VirtualBox from the Oracle website at this link:
As instructed on that site:
Add the public key with:
wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add - <enter>
Then install VirtualBox 5.1 by:
sudo apt-get update <enter>
sudo apt-get install virtualbox-5.1 <enter>
Download VirtualBox Extensions Pack from Oracle
wget - c http://download.virtualbox.org/virtualbox/5.1.24/Oracle_VM_VirtualBox_Extension_Pack-5.1.24-117012.vbox-extpack <enter>
Install the VirtualBox Extensions Pack from Oracle:
File -> Preferences -> Extensions
Select the add button
Choose the extensions file downloaded as previously stated and it will get installed.
Exit VirtualBox and restart it. You are now ready.
Settings during Windows 10 Insider Preview installation on VirtualBox
System -> Motherboard check Enable I/O APIC, Acceleration -> Hardware Virtualization, select Enable VT-x/AMD-V and Enable Nested Paging.
System -> Motherboard Chipset = ICH9
Create a Hard Disk as Fixed and not Dynamic to save time during installation.
Size about 25GB.