FiveTech Software tech support forums

You see, when BCA innocently partitions your hard drive to the inclusion of a new Windows “BOOTCAMP” partition, on the surface it appears to have formatted the BOOTCAMP partition into a FAT32 format in anticipation of the Windows.

Which is fine.

But what it also did (unfortunately) is inadvertently change the identification of your entire hard drive which was, for all intents and purposes a GPT disk into a Hybrid GPT/MBR disk.

The BCA partitioning process which converts your hard drive into a Hybrid MBR disk, creates this GPT error because OS X sees the Hybrid GPT/MBR disk as GPT whilst Windows 8/8.1 sees it as MBR and refuses to proceed with the installation because Window 8/8.1 insists it must sit on a GPT disk.

Solution?

We need to ‘re-tag’ the Hybrid GPT/MBR disk back to a GPT disk in order for Windows 8/8.1 be agreeable and compliant during the installation process.

if gdisk fails it may mean that csrutil status is enabled. Reboot Apple and run from the recover partition, open a terminal and do csrutil disable, then reboot and check from Apple if csrutil status is disabled. If so, then proceed with gdisk

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
Quit Terminal
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