Reverting Your Hybrid GPT/MBR Disk Back To a GPT Disk For Windows 7/8/8.1 Boot Camp Installation
Note: Whilst the following process is not destructive in nature we highly recommend you back up your data nonetheless to safeguard against any undesired results.
Download GPT fdisk utility (gdisk) from Sourceforge and install it
Launch Disk Utility (/Applications/Utilities/Disk Utility.app)
In the left pane select the Hard Drive (not Volume) which contains the OS X and BOOTCAMP partitions that BCA has created for you and click on the Disk Utility Info button (CMD+I)
In the Info window, note down the Disk Identifier value of your hard drive, e.g. in the example below the Disk Identifier is “disk0”
Launch Terminal (/Applications/Utilities/Terminal.app)
Launch gdisk in terminal by copying and pasting the following text into Terminal without the quotes, “sudo gdisk /dev/disk0”, enter your system admin password when prompted
In our example our Disk Identifier is “disk0”. Replace “disk0” with the corresponding Disk Identifier of your hard drive. For example, if your Disk Identifier is “disk1” then the appropriate Terminal command to launch gdisk would instead be “sudo gdisk /dev/disk1“.
Type “p” to view the partition table to confirm it is the correct hard drive you want to work on, if not type “q” to quit gdisk without making any changes and try again with another disk
Assuming you have the correct disk (i.e. entered the correct Disk Identifier to launch gdisk), type “x” to enter the experts menu
Type “n” to create a fresh protective MBR; note upon completion gdisk will not confirm a change or display any indication anything has been done, it will just show you another experts menu prompt
Type “w” to save the changes you have made, confirm this action when prompted to do so
Boot into OS X Recovery Mode (cmd+R).
Utilities menu > Terminal > Type:
Reboot your Mac whilst holding down the Option key and Boot into the “EFI Boot” disk to continue Windows 8/8.1 installation
Shutdown your Mac and unplug ALL other hard drives other than the hard drive you intend to install Windows 8/8.1 on. Also unplug all SSD cards or USB drives attached to your Mac
“We couldn’t create a new partition or locate an existing one. For more information see the Setup log files.”
Microsoft has piracy protections built into Windows 7/8/8.1 that prevents installation of Windows 7/8/8.1 on anything other than the primary boot disk/partition; if you do not unplug all other storage media during the Windows 7/8/8.1 the above error message will be displayed
Please leave a comment if you have discovered any other way around this nagging GPT issue but as far as we know this is the least destructive and surefire solution around the problem involving the least amount of effort and time.