Unsupported Disk Layout for UEFI firmware

Hi BobZ

Sounds like you are doing a clean install. Is that correct?

Yes your disk has to be GPT to clean install if you want to boot UEFI. Please ensure you have your personal data backed up before following steps below.

Boot with your media, on the first screen that appears press Shift + F10 to get command prompt. This will wipe your disk.

diskpart
List disk
select disk 0 (ensure zero is where you want to install, change to appropriate disk number)
clean
Convert gpt (if required for UEFI)
exit
exit

It is a good idea to just have your boot disk connected when installing, then connect other disks.

When doing a clean install please see this tutorial for BIOS recommendations.

Clean Install Windows 10

Exactly how are you trying to update to 1803 ?

Most modern pcs can boot into uefi or legacy bios depending in setting in the bios.

If set to UEFI, drive needs to be set to GPT, and if legacy bios, device needs to ve MBR.

However, some PCs are clever enough to boot from either MBR or GPT regardless of the bios setting i.e. bios setting may be UEFI but it will boot from an MBR drive.

However, when you come to upgrade or reinstall, the installer tries to use GPT if bios setting is set to UEFI and detects drive is MBR and fails with your message.

First thing to try is change bios setting to legacy bios, and it should work ok.

Don`t make any changes to anything until you tell us EXACTLY how you are trying to update to 1803.

OK, go into the Bios and set the Boot option/mode or however we want to word it to Legacy Mode.

Very strange you are getting that message if nothing was touched in the Bios.

It should just update.

Can you boot into windows ? Did it revert back yo 1709 ?

It would be great if you could post a shot of Disk Management, that would really help.

As I said earlier, if bios is set to uefi but pc is clever enough to boot from a legacy bios install with bios set to uefi, then you sometimes get this error mesage as the upgrader detects bios is set to uefi but drive is mbr but thinks it has to be GPT. Setting bios to mbr should sort issue, assuming drive is mbr formatted. You can check drive format in disk management.