Error: "We couldn't create a new partition or locate and existing one" installing Windows 8.1 via Bootcamp

Still it would be great if Apple wrote software that actually worked without you have to follow arcane links that aren't even mentioned during the process after the start screen - especially given how easy it is to end up with an orphaned partition that needs Gparted to recover & a full reinstall. Macs just work...riiiight. next machine is windows, my Mac adventures are done for life.

Hello,

I have just experienced this problem and worked out a fix. I have a late 2015 27" Retina iMac running el capitan

Looking at the disk it seemed to have a read only attribute and after you format it to NTFS it loses the label.

Therefore try these steps.

Run the BA and start the process

Follow it until you get the error

Then hit escape to exit setup and it takes you back to a screen with Install

At the bottom right is the repair computer part. Click this,

Go to the advanced options. I think there are 2 until you see the option for command prompt.

Open the command prompt

Then we will use DISKPART to reformat and label the partition.

***** IMPORTANT PLEASE MAKE SURE YOU SELECT THE CORRECT DISK AND THE CORRECT VOLUME ******

Once in disk part follow these commands

DISKPART> list disk

DISKPART> select disk (the number that matches your bootcamp partition)

DISKPART> attributes disk clear readonly

DISKPART> list volume

DISKPART> select volume (the number that matches your bootcamp volume)

DISKPART> format fs=ntfs label=BOOTCAMP quick

After the format exit diskpart and you should be left at a prompt similar to

X:/sources

just type setup to start setup and carry on as normal.

This time in setup select your partition now named BOOTCAMP but DO NOT FORMAT

Away you go.

Thanks

Madmaxious

What did the trick for me (installing Windows 10) was to do a PRAM reset before partitioning with Boot Camp Assistent, I tried it 10 times before and finally the pram reset did it. You can do it by holding CMD+OPTION+P+R while booting as long as you hear the boot sound at full volume, then release it and partition/install Windows using Bootcamp assistant.