Microsoft has announced the resolution of a critical bug affecting some commercial systems running Windows 11, which had rendered them unable to boot due to an “UNMOUNTABLEBOOTVOLUME” error. This issue arose following the installation of recent security updates and has been addressed in the February 2026 Patch Tuesday update.
The boot failure, which Microsoft had previously investigated, was linked to problematic updates from December 2025. It primarily impacted a limited number of commercial devices operating on Windows 11 versions 25H2 and 24H2.
In a private enterprise advisory reviewed by Susan Bradley of Ask Woody, the issue has now been officially marked as resolved with the release of the Windows 11 KB5077181 security update on February 10, 2026.
Devices affected by this boot issue experienced failures after the installation of the January 13, 2026, security update KB5074109 or subsequent updates. Users were met with a black screen accompanied by the message: “Your device ran into a problem and needs a restart. You can restart.” This left the systems inoperable, necessitating manual recovery efforts to restore functionality.
Microsoft had previously confirmed that the root cause of the issue stemmed from the failed installation of the December 2025 security update, which left devices in an improper state after the installation rolled back. This improper state could lead to further complications when attempting to install future Windows updates, potentially rendering the system unbootable.
Fix delivered in February Patch Tuesday update
Prior to the full resolution, Microsoft had released an initial fix in the optional non-security preview update KB5074105 on January 29, 2026. This update aimed to prevent additional systems from falling victim to the same bug.
With the release of the Windows 11 KB5077181 update during the February 2026 Patch Tuesday, Microsoft has confirmed that the issue is now fully resolved. “This issue is fully resolved in the Windows security update released on February 10, 2026 (the Resolved KBs listed above), and later updates,” stated Microsoft’s advisory.
However, devices that became unbootable prior to the fix may still require further remediation. Microsoft recommends that enterprise customers whose systems remain affected reach out to Microsoft Support for Business for assistance in restoring stability.
Interestingly, it remains unclear why Microsoft chose not to publicly share this advisory, a practice they typically follow for other known Windows issues.
