🛠 Fix Windows Server 2012 R2 VM Boot Error 0x7B on Hyper-V 2025

If you’ve recently migrated a physical Windows Server 2012 R2 machine to a Hyper-V 2025 environment and encountered a blue screen with the error code 0x0000007B (INACCESSIBLE_BOOT_DEVICE), you’re not alone. This guide walks you through a proven registry fix to resolve the issue.

⚠️ What Causes the 0x7B Error?

This error typically occurs when Windows cannot access the boot device. In the context of Hyper-V 2025, recent cumulative updates (e.g., KB5060842) have changed how virtual hardware is presented to guest VMs. As a result, Windows Server 2012 R2 may fail to recognize the boot device due to outdated or mismatched drivers.

✅ Step-by-Step Registry Fix (Offline Method)

Follow these steps to repair the registry and restore boot functionality:

Step 1: Boot into Windows Recovery Environment (WinRE)

1. Attach a Windows Server 2012 R2 ISO to the VM.
2. Boot the VM from the ISO.
3. On the setup screen, click Repair your computer.
4. Navigate to:\ Troubleshoot → Advanced Options → Command Prompt.

Step 2: Load the Offline Registry Hive

In the Command Prompt, type:

reg load HKLM\TempHive C:\Windows\System32\config\SYSTEM

Step 3: Copy Missing ACPI Device Keys

Run the following commands to replicate the necessary ACPI entries:

reg copy HKLM\TempHive\ControlSet001\Enum\ACPI\VMBus HKLM\TempHive\ControlSet001\Enum\ACPI\MSFT1000 /s

reg copy HKLM\TempHive\ControlSet001\Enum\ACPI\HyperVGenCounterV1 HKLM\TempHive\ControlSet001\Enum\ACPI\MSFT1002 /s

Step 4: (Optional) Ensure Storage Driver is Enabled

To ensure the Hyper-V storage driver is set to start at boot:

reg add HKLM\TempHive\ControlSet001\Services\storvsp /v Start /t REG_DWORD /d 0 /f

Step 5: Unload the Registry Hive

reg unload HKLM\TempHive

Step 6: Reboot the VM

shutdown /r /t 0

You can download the zip with the registry settings as a .reg file from https://itsimple.info/wp-content/uploads/2025/12/hyperv_2012r2_boot_fix-1.zip

including the missing driver file storvsp.sys should be in : c:\Windows\system32\drivers

🧪 After Reboot: What to Check

• The VM should boot normally.
• In Device Manager, confirm that:
  • “Microsoft Virtual Machine Bus” appears under System Devices.
  • No yellow exclamation marks are present.
• Registry path HKLM\SYSTEM\CurrentControlSet\Enum\ACPI should now include MSFT1000 and MSFT1002.

📝 Notes

• This fix addresses a compatibility issue introduced by Hyper-V 2025 updates.
• If the issue persists, consider uninstalling KB5060842 from the Hyper-V host or hosting the VM on an older Hyper-V version temporarily.
• There is already another post I have made regarding windows boot error after P2V : https://itsimple.info/?p=614