Microsoft Addresses Critical ACPI.sys Error in Windows 11 Virtual Environments After May 2025 Update

Microsoft has recently addressed a critical issue affecting Windows 11 systems, particularly those operating in virtual environments. The problem emerged following the deployment of the KB5058405 May 2025 security update, which led to startup failures and the display of a 0xc0000098 error associated with the ACPI.sys file.
Understanding the ACPI.sys Error
The ACPI.sys file is integral to Windows' power management and device configuration, functioning as the interface between the operating system and the ACPI BIOS. When this file encounters issues, it can result in system crashes during startup, as evidenced by the error message:

"Your PC/Device needs to be repaired. The operating system couldn't be loaded because a required file is missing or contains errors. File: ACPI.sys Error code: 0xc0000098"

This error predominantly affected virtual environments, including Azure Virtual Machines, Azure Virtual Desktop, and on-premises VMs hosted on Citrix or Hyper-V platforms. Microsoft acknowledged the issue, noting that it had limited impact on physical devices and was unlikely to affect PCs running Windows Home or Pro editions in home settings.
Microsoft's Response and Resolution
In response to the startup failures, Microsoft released the KB5062170 non-security out-of-band (OOB) update. This update is available for manual installation via the Microsoft Update Catalog. For organizations already impacted, Microsoft recommends utilizing Azure Virtual Machine repair commands to restore functionality. They also advise that environments yet to deploy the KB5058405 update should apply the OOB update instead to prevent potential issues.
Broader Implications and Preventative Measures
This incident underscores the complexities involved in managing updates within virtualized environments. It highlights the necessity for organizations to implement robust testing protocols before deploying updates, especially in critical systems. Regular monitoring of official channels for updates and patches is essential to maintain system stability and security.
For users encountering similar ACPI.sys errors, several troubleshooting steps can be considered:

• Update or Rollback ACPI Drivers: Ensuring that ACPI drivers are current can resolve compatibility issues. Conversely, if problems arise after an update, rolling back to a previous driver version may be beneficial.
• Run System File Checker (SFC) Scan: This built-in Windows tool scans and repairs corrupted system files, potentially addressing issues related to ACPI.sys.
• Check for Windows Updates: Keeping the operating system updated can resolve known issues and improve system stability.
• Modify BIOS/UEFI Settings: Adjusting settings such as disabling AHCI or updating the BIOS can sometimes rectify ACPI-related errors.

It's crucial to approach BIOS modifications with caution, as incorrect changes can lead to further system instability. Consulting official documentation or seeking professional assistance is advisable when making such adjustments.
In conclusion, while the recent ACPI.sys error presented significant challenges, Microsoft's prompt response and the availability of troubleshooting steps provide a pathway to resolution. This situation serves as a reminder of the importance of diligent update management and proactive system maintenance in both virtual and physical computing environments.

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Source: TechWorm Windows 11 Startup Issues Prompt Emergency Fix from Microsoft