VMs not booting after October 2023 Windows Updates
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Booting a VM and you get the error "Failed to power on with Error Incorrect Function"? Yeah, this hit us too. Looks like it hits VMs with secure boot enabled.
Quick fix: Move, delete or rename the .mrt & .rct files associated with the .vhdx file that the OS of the non-booting VM normally boots from. It'll then boot normally.
Alternatively you can uninstall the updates kb5031364 and/or kb5031361.