Ubuntu Error : "The partition table format in use on your disks normally requires you to create a separate partition for boot loader code"

If Windows 8 is pre-installed it is booting in UEFI mode and requires gpt partitioning.

But the error you are getting is because you are installing BIOS boot mode on a gpt partitioned drive. If you really want BIOS boot for Ubuntu then you need a tiny 1 or 2MB unformatted partition with the bios_grub flag in gparted. If you use gdisk to create partition it is code ef02. It actually is a very long GUID that is assigned with these short flags or codes.

But you probably do not want Ubuntu in BIOS boot and Windows in UEFI boot. You may have to go into UEFI boot menu and turn on/off UEFI or CSM/BIOS each time you reboot into the other system. Much better to install Ubuntu in UEFI boot mode.

How you boot install media is how it installs. Your UEFI boot menu for the Ubuntu installer with have two entries. One will say UEFI and name of flash drive and the other just the name of flash drive which then is BIOS boot.

Shows install with screen shots. Both BIOS purple accessibility screen & UEFI black grub menu screen

https://help.ubuntu.com/community/UEFI

Also shows Windows 8 screens

Installing Ubuntu Alongside a Pre-Installed Windows with UEFI

UEFI install,windows 8 with Something Else screen shots

http://www.everydaylinuxuser.com/2014/05/install-ubuntu-1404-alongside-windows.html

Linux on UEFI: A Quick Installation Guide

http://www.rodsbooks.com/linux-uefi/