If you see a partition alert while using Boot Camp to install Windows
Learn what do if you see an alert that says "We couldn't create a new partition or locate an existing one" while you're using Boot Camp to install Windows 8 or Windows 10 on your Mac.
This alert might appear if any Thunderbolt or USB storage devices (other than the USB media that contains a Windows ISO installer) are connected to your computer during the install process. You can fix the error with these steps:
Shut down your Mac.
Disconnect all Thunderbolt and USB storage devices, except for the USB media that contains the Windows ISO installer.
Try the installation again.
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