Solution to INACCESSIBLE_BOOT_DEVICE error on Windows 10 installed on Bootcamp Partition

I thought it would be helpful to share with the community as to how I was able to fix the foregoing issue on my Macbook 12" (2015) after upgrading to OSx Mojave.

Apparently, when upgrading to Mojave, the bootcamp partition was affected in a way that Windows was no longer identify the hard drive that it was installed on because presumably the upgrade process sometimes "deletes" or "removes" or "fails to install" a correct mass storage device driver that lets Windows access or "see" the Mac's internal hard drive.

In this case, it triggers Windows to start up with a INACCESSIBLE_BOOT_DEVICE error. This error is caused by the lack of the correct mass storage device driver. To resolve this issue, the correct mass storage device driver can be injected into Windows.

What is needed

1. USB Flash drive (8 GB or larger recommended)
2. Windows Installer ISO for Windows 10
3. Boot Camp drivers

USB Flash Drive

1. Insert an 8GB or larger flash drive into a USB port on the Mac
2. In Disk Utility, format the Flash drive as exFAT. Quit Disk Utility after this operation completes.

Boot Camp Driver

Open Boot Camp Assistant in the Utilities folder, and download the current Windows Support Software from the Action menu to your desktop or other location. Do save directly to the USB Flash Drive.

Windows Install Media

Download the current install media (i.e an ISO file for both 32-bit and 64-bit machines) from the Microsoft website at https://www.microsoft.com/en-us/software-download/windows10ISO

Create Recovery USB Flash Drive

TwoCanoes has also published a page on how to Create a Windows 10 Bootable USB Flash Drive on a Mac. Here is a quick summary, so all of the relevant instructions are in the same place:

1. Mount the Windows ISO that was downloaded from Microsoft.
2. Drag all the files and folders from the mounted ISO to the USB Flash Drive.
3. Drag the contents of the Windows Support Software to the USB Flash Drive.
4. If there is not an AutoUnattend.xml at the top level of the drive (as shown below), download AutoUnattend.xml, unzip it, and add it to the drive. AutoUnattend.xml provides the location of the $WinPEDriver$ folder to load the drivers during boot.
5. The 2018 MacBook Air (and potentially Macs after that) have cannot load the IntelMEI driver and give a “Windows Setup could not install one or more boot-critical drivers. To install Windows, make sure that the drivers are valid, and restart the installation”. On the USB Flash drive, open the $WinPEDriver$ and remove the IntelMEI folder.

Once the Flash drive has been created, it should look like this:

The $WinPEDriver$ folder is important because the $WinPEDriver$ folder contains the drivers for Windows to boot successfully from the USB Flash drive and the hardware on that Mac.

Boot from the USB Flash drive

To inject the drivers, the Mac must be booted from the USB Flash drive.

1. Insert the USB Flash drive into an available USB port on the Mac
2. Reboot while holding the option key.
3. Select EFI volume in the startup selector.

Inject drivers

Once booted from the USB Flash drive, the correct Windows drivers can be injected into the version of Windows that is experiencing the INACCESSIBLE_BOOT_DEVICE error.

1. Press fn-shift-f10 (or just shift-f10 depending on your keyboard) to open the Windows command line interface.
2. Typically, the USB Flash drive is assigned C: and the internal drive is assigned D: when booted from the USB Flash Drive. Verify drive lettering by entering in these commands and verifying correct driver letter assignment. If the drive letters are different, adjust the dism command below to use the correct lettering. On C: you should see a $WinPEDriver$ folder (and other items) and on D: you should see a Windows folder and Users folder (and other items).dir c:
3. dir d:
4. Inject Windows drivers by running the following command (note that there is a space before every forward (“/”) slash.

dism /Image:D:\ /Add-Driver /driver:c:\$WinPEDriver$ /recurse

Once completed, close all the windows by clicking X in the upper right hand corner of all the open windows, and the Mac will shut down. Remove the USB Flash drive, and restart into Windows by holding the option key as you turn on Mac and select your Windows partition.

For the source of this information, you can go to the TwoCanoes blog at https://twocanoes.com/knowledge-base/resolving-inaccessible_boot_device-error-after-restoring-winclone-image/.