"Boot Camp installation failed" errors appear when you perform a new installation of Windows 10 using the October 2018 edition on a Mac with an earlier version of macOS.
Update macOS to avoid the issue
You can avoid these errors by updating your Mac to the latest version of macOS Mojave before you install Windows.
If you need to install Windows on a Mac that's not running the latest version of macOS, first install the April 2018 edition using Boot Camp Assistant. Then use Windows Update to install the October 2018 edition.
If you've already attempted a new installation of the October 2018 edition of Windows 10 and Boot Camp Assistant has frozen or shown error messages, follow the steps below.
Remove partitions, then reinstall
If you try to perform a new installation of Windows 10 using the October 2018 edition on a Mac with an earlier version of macOS, this error appears: "Boot Camp installation failed. An error occurred while copying the Windows installation files."
After showing this error message, Boot Camp Assistant might stop responding. Use Force Quit to close the app. When you open Boot Camp Assistant again, an error says "The startup disk cannot be partitioned or restored to a single partition."
Follow these steps to fix the issue:
- Go to the Microsoft Download Windows 10 Disc Image (ISO File) page. In the menu under Select edition, select the Windows 10 April 2018 Update. Then follow the steps to download the ISO file.
- Open Disk Utility.
- In the Disk Utility menu bar, click Partition. If you see a dialog asking whether you want to add a volume or partition, click Partition.
- In the graph that appears, select OSXRESERVED, then click the remove (minus) button.
- In the same graph, select BOOTCAMP, then click the remove (minus) button.
OSXRESERVED and BOOTCAMP are empty partitions that Boot Camp Assistant created during the attempted installation.
- Click Apply, then click Partition to confirm.
- Open Boot Camp Assistant and try the installation again, making sure to use the Windows 10 April 2018 Update ISO file.
After the installation is complete, you can update to the October 2018 edition using Windows Update.