Problem while installing Windows 7 in VirtualBox

If you want to install Windows 7 via Oracle VirtualBox, you could get a error message like this:

Status: 0xc0000225
Info: An unexpected error has occurred

The installation stops and you have no idea what's going on.

The solution is quick and easy:

• Shutdown the virtual machine
• In the main menu choose "System", click the Mainboard / Motherboard tab
• Check the "Activate IO-APIC" Box. 
• That's it! Save it and install your system.