Unable to mount the WIM, so the update process cannot continue – MDT on Hyper-V

Not the first time I’ve run into this issue and probably won’t be the last! While building a new Windows Server 2016 (Full) Microsoft Deployment Toolkit server when attempting to run the ‘Update Deployment Share’ wizard I was getting the following error message.

Unable to mount the WIM, so the update process cannot continue.

The solution is simple; if you are running this machine on Hyper-V (presumably other Hypervisors as well) you will need to shutdown the VM, disable Secure Boot (on the VM only) and then power it back on. The next time you run the wizard it will complete as normal.

The error message in full context for reference.

=== Making sure the deployment share has the latest x86 tools ===
=== Making sure the deployment share has the latest x64 tools ===

=== Processing LiteTouchPE (x64) boot image ===

Building requested boot image profile.
Determining if any changes have been made in the boot image configuration.
No existing boot image profile found for platform x64 so a new image will be created.
Calculating hashes for requested content.
Changes have been made, boot image will be updated.
Windows PE WIM C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\Windows Preinstallation Environment\amd64\en-us\winpe.wim will be used.
Unable to mount the WIM, so the update process cannot continue.

=== Completed processing platform x64 ===

 

=== Processing complete ===