Windows: Some users may lose “access to the C: drive” and experience “app failures”

Microsoft confirmed a new Windows issue on March 12th, 2026 that prevents access to files on the main c: drive of the system and blocks certain applications from launching.

The issue affects certain Samsung devices that run Windows and have installed the February 2026 security updates or newer updates for Windows 11, version 24H2 or 25H2 systems.

Here are the details:

• Affected Windows versions: Windows 11, version 24H2 and 25H2
• Affected devices: Only certain Samsung devices.
• Originating update: KB5077181 (25H2 and 24H2)

Affected users may get the error message “C:\ is not accessible – Access denied” after installation of the update on affected devices. This prevents access to files on the drive and will also block some applications from launching. Microsoft mentions Outlook, Office apps, web browsers and system utilities specifically.

The problems do not require specific user actions. They occur during common actions, such as trying to access files, starting programs, or performing administrative tasks. Furthermore, users may also be blocked from elevating privileges, uninstalling, updates, or collecting logs due to permission failures.

Microsoft says that it is investigating the issue and that it suspects that the Samsung Share application is causing the issue. There is no workaround at the time of writing, but uninstalling the update — if possible — may resolve the issue. However, this leaves the system open for potential attacks, as it won’t have the February and March 2026 security issues patched anymore.

Affected users and administrators may want to keep an eye on the Windows 11 release information page. Microsoft will update the page when it has a workaround or a solution.