Some Windows 11 users have run into a serious problem in recent days. A software bug that can block access to the main system drive. Microsoft has acknowledged the issue and says it’s working on a fix. The problem appears to have been introduced with the February 2026 security update KB5077181. Affected users see the error message “C:\ is not accessible, Access denied”, which prevents them from opening files, launching apps, or even performing certain system tasks.
Reports indicate the issue is hitting Samsung laptops the hardest. Microsoft says it may be connected to the Samsung Share app, though the exact cause hasn’t been confirmed yet. The bug seems to affect systems running the latest Windows 11 releases, versions 24H2 and 25H2. Microsoft also says users in several regions, including Brazil, Portugal, Korea, and India, have reported the problem.
For those impacted, the result can be severe. Since the C: drive holds the operating system and most applications, losing access to it can make the PC nearly unusable. For now, Microsoft suggests rolling back the February update if you’re experiencing the issue. You can do this through Settings | Windows Update and uninstall the latest update. If you haven’t installed it yet, it may be worth pausing updates until a fix arrives.
Some users online have shared workaround ideas, including changing ownership of the C: drive. However, these fixes carry risks and aren’t officially recommended, so they should be attempted with caution.
Here’s the tutorial on how to uninstall an update using Windows Recovery Environment.